Evidence and Mechanism by which Upper Partial Fibulectomy Improves Knee Biomechanics and Decreases Knee Pain of Osteoarthritis

Yong Nie; ZeYu Huang; Bin Xu; Bin Shen; Virginia Byers Kraus; FuXing Pei

doi:10.1002/jor.23867

. Author manuscript; available in PMC: 2020 Sep 9.

Published before final editing as: J Orthop Res. 2018 Feb 9:10.1002/jor.23867. doi: 10.1002/jor.23867

Evidence and Mechanism by which Upper Partial Fibulectomy Improves Knee Biomechanics and Decreases Knee Pain of Osteoarthritis

Yong Nie ^1,^†, ZeYu Huang ^1,^2,^†, Bin Xu ^1,^†, Bin Shen ¹, Virginia Byers Kraus ^2,^3,^**, FuXing Pei ^1,^*

PMCID: PMC7480762 NIHMSID: NIHMS1620805 PMID: 29424452

Abstract

To investigate the change in short-term clinical outcomes and biomechanical properties of the knee in response to upper partial fibulectomy and to probe into the biomechanical mechanism underlying the clinical benefits of upper partial fibulectomy for medial compartment knee osteoarthritis (KOA). 29 patients with medial compartment KOA underwent upper partial fibulectomy. Visual analog scale (VAS) pain, the hospital for special surgery knee score (HSS), hip-knee-ankle (HKA) angle (measured in the frontal plane), and flexion/extension range of motion of the knee were assessed before and up to 6 months after surgery. Patients and 20 healthy controls were evaluated by 3D gait analysis and dynamic lower limb musculoskeletal analysis. Both VAS pain and HSS score were significantly improved (P <0.001) one day after surgery and steadily improved during the subsequent 6 months. HKA angle improved (P=0.025) immediately and remained stable by 3 months after surgery. The decreased overall peak KAM (decreased by 11.1%) and increased HKA angle (increased by 1.80 degrees from a more varus to more neutral alignment) of affected and operated side by 6 months after surgery were observed. Muscle activity of biceps femoris caput longum of affected and operated side increased immediately and was equivalent to healthy controls by 6 months after surgery (P=0.007). This pilot study provides biomechanical evidence of benefit from partial upper fibulectomy and indicates a plausible rationale for the improvement in clinical symptoms. Long-term clinical outcomes and precise biomechanical mechanism of partial upper fibulectomy should be further investigated.

Keywords: medial compartment knee osteoarthritis, upper partial fibulectomy, gait analysis, knee adduction moment, musculoskeletal analysis

Introduction

A substantial proportion (12.1%) of the population aged 60 years and older is affected by symptomatic radiographic knee osteoarthritis (KOA) [1]. Total knee arthroplasty (TKA) or unicompartmental knee arthroplasty (UKA) are the most common surgical procedures for patients with end-stage KOA. However, given the limited lifespan of implants, which is particularly problematic for younger patients, and the associated economic burden of OA, it is imperative to implement treatment approaches that effectively slow disease progression [2, 3].

The compartments of the knee are not all affected in the same way; people are at 10 times greater risk of having medial than lateral KOA [4]. Indeed, during walking, the medial compartment supports 2.2 times as much loading as the lateral compartment [5, 6]. Excessive loading and alterations in load distribution within the knee joint are believed to play major roles in the progression of articular cartilage degradation [7–10]. Accordingly, several conservative treatments that alter abnormal loading patterns are used to reduce pain and improve function within the knee joint. One such treatment is gait modification; for instance, the toe-out gait modification is proven to be feasible and may provide long-term biomechanical and clinical benefits for people with KOA [11]. A valgus knee brace is another treatment recommended to manage medial KOA. It uses a three-point bending system and generally reduces medial knee load and pain during weight bearing on the affected leg [12]. Another conservative treatment, lateral wedge insoles, are reported to be effective in the treatment of medial KOA in some studies [13] but their efficacy has not been supported by a high quality, 12-month, randomized controlled clinical trial [14].

The fibula is a valuable source of bone graft. Partial and total fibulectomy are performed as part of some procedures, including upper tibial osteotomy and surgical treatment of tibial nonunion [15, 16]. Recently, upper partial fibulectomy has been found to relieve pain and improve function of patients with medial compartment KOA. Yang et al. [17] used upper partial fibulectomy to treat 156 patients with medial compartment KOA; after more than two years follow-up, proximal fibular osteotomy significantly improved both the radiographic appearance and function of the affected knee joint and led to long-term pain relief. Chen et al. [18] studying the mechanism by which upper partial fibulectomy may benefit medial compartment KOA, suggested that upper partial fibulectomy caused the transfer of load from the medial to the lateral tibial plateau thereby resulting in pain relief. Improvement in long-term clinical outcomes in response to upper partial fibulectomy are suggested to be related to beneficial changes in bone remodeling, muscles and ligaments. However, the previous studies lack sufficient quantitative evidence to explain the precise biomechanical mechanism underlying the clinical benefits of upper partial fibulectomy for medial compartment KOA.

Therefore, the objective of this pilot clinical and biomechanical study was to investigate changes in clinical outcomes and joint biomechanics, including 3D gait analysis and lower limb musculoskeletal analyses, due to upper partial fibulectomy for patients with medial compartment KOA. We also attempted to explain the biomechanical mechanism underlying the clinical benefits of upper partial fibulectomy for medial compartment KOA. We hypothesized that after upper partial fibulectomy, the increased freedom of the proximal fibula may lead to competition of muscles (Biceps femoris versus Peroneus) attached to the fibular head that creates a tension in the lateral knee. This lateral tension may cause improvement in HKA angle from a more varus to more neutral alignment and thereby reduce medial compartment loading.

Methods

This was a prospective study with two levels of evidence.

Participants

Community-dwelling individuals with medial compartment knee OA were recruited from the participant database of our hospital and via advertisements in print media. A diagnosis of OA was made by an expert orthopaedic surgeon using the American College of Rheumatology criteria for the classification and reporting of OA of the knee joint [19]. Inclusion criteria included: (1) radiological findings consistent with medial compartment dominant knee OA based on Kellgren-Lawrence grade [20] as follows, grade two (small osteophytes, possible narrowing of the joint space), or grade three (multiple, moderately sized osteophytes, definite joint space narrowing, some sclerotic areas, possible deformation of bone ends); (2) predominance of self-reported pain over the medial aspect of the knee; (3) knee pain unresponsive to conventional medical treatments for at least three months. Exclusion criteria included: (1) symptomatic comorbid disease that limited walking more than knee pain limited walking (diabetic neuropathies, inflammatory arthritis, foot ulcers or sores); (2) knee surgery or intra-articular injection within the prior 6 months; (3) current or past (within the prior 6 weeks) oral corticosteroid use; (4) history of prior knee joint replacement or tibial osteotomy of the index knee; (5) valgus knee or any other condition affecting lower limb function. The study was approved by the Institution’s Clinical Research Ethics Board and all participants provided written informed consent.

Study design

Participants who met the prespecified inclusion and exclusion criteria listed above were initially invited to the gait laboratory for the preoperative assessment, which included pain and physical function assessment, limb alignment determination, 3D gait and musculoskeletal analysis. The clinical indices were measured by a single investigator (BX). The 3D gait and lower limb musculoskeletal analyses were performed by a single biomechanical expert (YN), who was blinded to clinical outcomes. The patients then underwent upper partial fibulectomy at a single center, performed by a single orthopaedic surgeon (FXP) responsible for verifying the diagnosis of OA. Participants returned on day one, 3 months and 6 months after surgery to the laboratory for follow-up testing that included the same items as those in the preoperative assessment. In addition, 20 healthy controls (10 males and 10 females) were included for biomechanical analyses.

Surgical procedure and perioperative management

Local anesthesia with 2% lidocaine was administered between 5–11 cm from the fibular head. An incision, between 6–10 cm from the fibular head was carried out along the fibula. Tissue separation was carried out to identify the inter-muscular space between the extensor digitorum longus and peroneus longus/ peroneus brevis. The upper section of the fibula was exposed from the inter muscular space, and an osteotomy of 1 cm was performed between 7–8 cm from the proximal fibular head (Figure 1A&B). The broken end of the fibula was enclosed with bone wax. After a local tissue rinse with normal saline, hemostasis and incision closure were achieved. Local compression around the incision was achieved with an elastic bandage. After the operation, the diet was restored, and supervised exercise was carried out to strengthen the quadriceps femoris muscle and the muscle groups around the knee. On the second day, the patients were recommended to walk and return to normal life. Patients were encouraged to leave the hospital no earlier than the second day after the operation. At this time, they could walk freely without a walking aid, and had no signs of serous drainage, incision secretion or local swelling at the incision site. The average hospitalization time was 4.36± 1.25 days including the preoperative stay (about 3 days in our hospital) for the preoperative examinations.

Figure 1A-D. — Knee joint antero-posterior radiographs, 3D gait analysis and Inverse dynamic analysis of lower limb musculoskeletal model. Knee radiograph before (A) and after (B) upper partial fibulectomy. (C). Schema of 3D gait analysis. (D). Inverse dynamic analysis of lower limb musculoskeletal model.

Pain and physical function assessment, limb alignment measurement

Patient self-reported pain during movement was measured by visual analog scale (VAS) from zero to 10 in 1 cm intervals (zero: no pain, 10: greatest pain imaginable). The hospital for special surgery (HSS) knee score was used to investigate functional status [21]. The mechanical axis (hip-knee-ankle or HKA angle) was used to assess limb alignment from a long-limb radiograph. The HKA angle was defined as the angle between the mechanical axes of the femur and the tibia (from the center of the femoral head to the midpoint of the tibial plateau and from the midpoint of the tibial plateau to the midpoint of the ankle) and measured in the frontal plane from a full-length lower-limb radiograph during standing. In addition, passive flexion/extension range of motion (ROM) of the knee joint was measured using a standard clinical goniometer with the patient lying supine.

3D gait analysis

Each subject walked at a self-selected pace on a 12-m walkway wearing 28 retro-reflective markers to track the motions of the pelvis, each thigh, lower leg and foot [22] (Figure 1C). An initial standing static trial was performed using an additional 10 markers placed over the ankle, femoral epicondyles and greater trochanter to determine segment orientations. Three-dimensional trajectories of the markers were collected at 290 Hz using a 10-camera motion analysis system (Oqus300, Qualisys, Gothenburg, Sweden). Ground reaction forces (GRF) were recorded with two force plates (Bertec, Columbus, OH, USA) incorporated into the walkway. Each patient performed five gait trials (the first two trials were for the purpose of adaption to the testing procedures and were not included in the final results) and was instructed to walk as naturally as possible looking straight ahead [23]. Our gait laboratory was equipped with a synchronous video camera enabling us to acquire videos (under IRB approval) of 13 subjects.

Inverse dynamic techniques and commercially available software (Visual 3D, C-Motion, Inc., Rockville, MD, USA) were used to calculate five gait variables including the following: gait speed, single-limb stance time, sagittal (flexion/extension) plane knee ROM during walking and overall peak knee adduction moment (KAM) for both sides. The gait speed was divided by body height to generate a normalized value for comparing between subjects. The mean value from three trials was calculated for each variable. For the control group, each of the gait variables was calculated for each limb and then averaged across limbs for each trial.

Lower limb musculoskeletal modeling

For each subject, a subject-specific musculoskeletal model of the lower limb was built in the AnyBody Modeling System (AMS) (version 6.0.5.4379, AnyBody Technology A/S, Aalborg, Denmark) using the Anybody Managed Model Repository (AMMR) version 1.6.4. The lower extremity model included a total of 110 constant strength muscles divided into 318 individual muscle paths (55 muscles and 159 muscle paths for each leg), 6 joints and 7 degrees of freedom for each leg. Estimating the muscle forces responsible for dynamic human motion is one of the inherent problems in musculoskeletal modeling. The muscular load sharing problem in AMS is solved by minimizing an optimality criterion at each instant of the movement [24]. The mechanical and mathematical methods behind AMS were explained in detail by Damsgaard et al. [24]. The measured kinetic and kinematic data were then imported from the C3D file into AMS and smoothed with a low-pass filter (zero-lag fourth-order Butterworth filter) with a cutoff frequency of 12 Hz and 10 Hz, respectively. The kinetic data were down-sampled to 250 Hz and synchronized in time with the kinematic data. These data were processed in AMS to drive the three-dimensional gait model [25] (Figure 1D). In addition, the same 20 healthy controls (10 males and 10 females) were also included.

Two muscles (biceps femoris and peroneus longus) attached to the fibular head were assessed for each subject. Muscle activity (the ratio between muscle force and muscle strength) was calculated. The mean value from three trials was calculated for muscle activity. For the control group, muscle activity was calculated for each limb and then averaged across limbs for each trial.

Statistical analysis

Differences in the longitudinal outcome data were assessed by repeated measures ANOVA with Bonferroni post-hoc tests for clinical outcomes of the affected (operated) side, 3D gait and musculoskeletal outcomes of the affected (operated) and unaffected (unoperated) sides. Gait and musculoskeletal differences between patients and controls were assessed using independent t tests for two critical time points (preoperative and 6 month postoperative conditions). The differences of demographic data between patients and controls were also assessed using independent t tests. Statistical analyses were performed using SPSS version 19.

Results

Between May 2015 and May 2016, 29 patients (22 females and 7 males) were included with medial compartment dominant knee OA who underwent upper partial fibulectomy and received preoperative, day one, 3 months and 6 months follow-up assessments. The mean age, body weight and height were 58.45 ± 13.82 (ranging from 42 to 85 years old), 61.82 ± 8.42 (ranging from 50 to 76 kg) and 158.91 ± 3.24 (ranging from 150 to 165 cm), respectively. 5 knees were KL grade 2; 24 knees were KL grade 3. The average surgical time was 25.57 ± 5.21 min. In addition, the mean age, body weight and height of 20 healthy controls were 27.27 ± 3.20 (ranging from 23 to 32 years old), 62.09 ± 12.00 (ranging from 52 to 90 kg) and 165.36 ± 6.34 (ranging from 153 to 173 cm), respectively. Significant difference was observed in age between patients and controls.

Clinical outcomes

By repeated measures ANOVA, compared to preoperative values, significant differences (p<0.001) were seen in the longitudinal outcome data with regard to VAS score (at 1 day, 3 and 6 months), HSS score (1 day, 3 and 6 months) and HKA angle (1 day, 3 and 6 months). Upper partial fibulectomy resulted in a significant improvement in HKA angle (p=0.025) from a varus to a more neutral (mean 0.70 degrees change) alignment postoperatively (Table 1). No significant difference was seen in passive flexion/extension knee ROM over any time interval.

Table 1.

Pain, physical function and limb alignment before, one day, 3 months and 6 months after upper partial fibulectomy

Variable	Pre (n=29)	Post-1day (n=29)	Post-3months (n=29)	Post-6months (n=29)	P value (P1)	P value (P2)	P value (P3)	P value (P4)
VAS score	5.50 (1.16)	1.25 (0.89)	0.67 (1.11)	0.17 (0.74)	< 0.001	0.256	0.195	< 0.001
HSS score	64.50 (8.32)	86.67 (5.47)	92.83 (3.86)	93.33 (3.02)	< 0.001	<0.001	0.032	< 0.001
HKA angle (°)	178.01 (2.09)	178.71 (2.17)	179.23 (2.04)	179.81 (1.91)	0.025	0.134	0.116	< 0.001
Passive ROM (°)	123.75 (12.31)	124.17 (12.45)	125.83 (10.32)	125.83 (10.30)	0.318	0.745	0.331	0.154

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Pre: Before upper partial fibulectomy; Post-1day: One day after upper partial fibulectomy; Post-3months: 3 months after upper partial fibulectomy; Post-6months: 6 months after upper partial fibulectomy; P1: Comparing Pre and Post-1day; P2: Comparing Post-1day and Post-3months ; P3: Comparing Post-3months and Post-6months; P4: Comparing Pre and Post-6months; VAS: Visual analog scale; HSS: Hospital for special surgery knee score; HKA: Hip-Knee- Ankle angle; Passive ROM: Passive flexion/extension knee range of motion

Means (standard deviations) are provided above for pain, function and limb alignment.

At the 3-month and 6-month follow-up visits, VAS pain and HSS scores improved still further (Figure 2A&B). No significant further change was noted in HKA angle from 3 months after operation to the 6-month follow-up assessments with postoperative status changing a mean 1.80 degrees overall from a more varus alignment at baseline to a more neutral alignment (Figure 2C).

Figure 2A-H. — Changing trend of clinical and 3D gait outcomes before upper partial fibulectomy and during the 6 months follow-up. (A). VAS score. (B). HSS score. (C). HKA angle. (D) Passive ROM. (E) Gait speed. (F). Stance time. (G). Active ROM. (H). Overall peak KAM.

VAS: Visual analog scale; HSS: Hospital for special surgery knee score; HKA: Hip-Knee- Ankle angle; Passive ROM: Passive flexion/extension knee range of motion; Active ROM: Flexion/extension knee range of motion during walking; KAM: Knee adduction moment; Affected: operated side; Unaffected: unoperated side; m: month.

3D gait analysis

Although there were no significant differences in the four 3D gait parameters from the preoperative and 6 months’ postoperative time points, significant differences were observed in the longitudinal outcome data with regard to gait speed (1 day) and active flexion/extension knee ROM (1 day) during walking for the affected (operated) side (Table 2). Change tendencies of all four 3D gait parameters for the longitudinal time points were shown in Figure 2. Gait speed and active flexion/extension knee ROM of both sides gradually improved from day one to 6 months after surgery (Figure 2E&G). The overall peak KAM of both sides decreased immediately on day one after surgery (both the affected and unaffected sides decreased by 8.9% and 9.0%, respectively) and then tended to remain stable at the immediate postoperative level, although no significant difference was found (Figure 2H). Stance time of the two sides were different. The stance time of the unaffected (unoperated) side increased day one after surgery, and then steadily decreased. However, the stance time of the affected (operated) side was not significantly changed by day one after surgery, but was subsequently restored to the same level as the unaffected (unoperated) side at 3 months after surgery (Figure 2F).

Table 2.

Gait parameters before, one day, 3 months and 6 months after upper partial fibulectomy

Gait parameter	Sides	Pre (n=29)	Post-1day (n=29)	Post-3months (n=29)	Post-6months (n=29)	P value (P1)	P value (P2)	P value (P3)	P value (P4)
Speed (Statures/s)	Both	0.51 (0.09)	0.41 (0.09)	0.51 (0.10)	0.57 (0.09)	< 0.001	< 0.001	0.413	0.321
Stance time (Cycle time%)	Affected	62.74 (2.09)	62.68 (4.17)	65.45 (2.30)	62.53 (1.83)	0.962	0.464	0.008	0.856
Active ROM (°)	Affected	61.34 (7.30)	52.97 (10.64)	63.30 (5.80)	65.03 (2.68)	0.025	0.018	0.342	0.349
Overall peak KAM (Nm/kg)	Affected	0.45 (0.15)	0.41 (0.16)	0.40 (0.09)	0.40 (0.18)	0.410	0.566	0.757	0.365
Stance time (Cycle time%)	Unaffected	63.66 (2.82)	67.07 (6.92)	63.75 (1.48)	61.75 (1.75)	0.137	0.037	0.135	0.425
Active ROM (°)	Unaffected	62.21 (6.38)	60.71(7.32)	65.75 (4.45)	67.00 (3.98)	0.685	0.432	0.612	0.334
Overall peak KAM (Nm/kg)	Unaffected	0.44 (0.13)	0.40 (0.11)	0.40 (0.02)	0.41 (0.15)	0.116	0.755	0.668	0.503

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Pre: Before upper partial fibulectomy; Post-1day: One day after upper partial fibulectomy; Post-3months: 3 months after upper partial fibulectomy; Post-6months: 6 months after upper partial fibulectomy; Affected: Affected and operated side; Unaffected: unaffected and unoperated side; Active ROM: Flexion/extension knee range of motion during walking; KAM: Knee adduction moment; P1: Comparing Pre and Post-1day; P2: Comparing Post-1day and Post-3months ; P3: Comparing Post-3months and Post-6months; P4: Comparing Pre and Post-6months.

Means (standard deviations) are provided above for gait parameters.

Compared with healthy controls, preoperative assessments showed that the KOA patients had less efficient gait (based on gait kinematic parameters including walking speed, joint range of motion and stance time of both sides) and higher overall peak KAM for both sides. By 6 months after surgery, the operated knee OA patients showed gait patterns similar to healthy controls (Table 3).

Table 3.

Gait parameters between healthy controls and patients assessed before and 6 months after upper partial fibulectomy.

Gait parameter	Control (n=20)	P value (Pre vs Control)		P value (Post-6 months vs Control)		P value (Pre ) Between two sides	P value (Post-6 months) Between two sides

		Affected	Unaffected	Affected	Unaffected
Speed (Statures/s)	0.73 (0.12)	<0.001		0.048		-	-
Stance time (Cycle time%)	62.08 (1.92)	0.356	0.072	0.669	0.832	0.254	0.765
Active ROM (°)	70.36 (3.92)	0.001	< 0.001	0.016	0.236	0.479	0.810
Overall peak KAM (Nm/kg)	0.33 (0.10)	0.018	0.026	0.178	0.324	0.665	0.521

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Pre: Before upper partial fibulectomy; Post-6months: 6 months after upper partial fibulectomy; Affected: Affected and operated side; Unaffected: unaffected and unoperated side; Active ROM: Flexion/extension knee range of motion during walking; KAM: Knee adduction moment.

Means (standard deviations) are provided above for gait parameters.

Lower limb musculoskeletal model dynamic analysis

Although only the peak muscle activity of the biceps femoris caput longum of the affected (operated) side showed significant differences from the preoperative to 1 day, 3 and 6 months’ postoperative timepoints, significant differences (p<0.05) were also observed for longitudinal changes in peak muscle activity of the peroneus longus of the affected (operated) side (at 1 day). Peak muscle activity of the biceps femoris caput longum of the affected (operated) side increased immediately and remained high at 6 months (P=0.007) after surgery, while that of the peroneus longus decreased immediately one day after surgery and then recovered gradually. Compared with healthy controls, preoperative assessments showed that the KOA patients had significantly lower (P<0.05) peak muscle activity of the biceps femoris and higher peak muscle activity of the peroneus longus for the affected (operated) side. However, these differences were not obvious by 6 months after surgery. In addition, no significant differences were found for the longitudinal outcomes related to the unaffected (unoperated) side or comparing the unaffected (unoperated) side to healthy controls (Table 4 & Figure 3).

Table 4.

Peak muscle activity during gait before, one day, 3 months and 6 months after upper partial fibulectomy

Muscles	Control (n=20)	Sides	Pre (n=29)	Post-1day (n=29)	Post-3months (n=29)	Post-6months (n=29)	P value (P1)	P value (P2)	P value (P3)	P value (P4)
Biceps femoris (Caput Longum)	0.12 (0.03)	Affected	0.10 (0.02)	0.15 (0.06)	0.14 (0.04)	0.13 (0.03)	0.048	0.007	0.040	0.327
Biceps femoris (Caput Breve)	0.04 (0.01)	Affected	0.03 (0.004)	0.03 (0.012)	0.03 (0.007)	0.03 (0.005)	0.704	0.374	0.001	0.108
Peroneus longus	0.17 (0.06)	Affected	0.21 (0.10)	0.07 (0.03)	0.14 (0.04)	0.20 (0.10)	0.034	0.477	0.399	0.453
Biceps femoris (Caput Longum)	0.12 (0.03)	Unaffected	0.11 (0.02)	0.10 (0.03)	0.12 (0.03)	0.12 (0.03)	0.847	0.053	0.391	0.686
Biceps femoris (Caput Breve)	0.04 (0.01)	Unaffected	0.03 (0.008)	0.03 (0.008)	0.03 (0.007)	0.03 (0.004)	1.000	1.000	0.239	0.081
Peroneus longus	0.17 (0.06)	Unaffected	0.19 (0.08)	0.25 (0.11)	0.24 (0.08)	0.19 (0.09)	0.317	0.587	0.636	0.568

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Pre: Before upper partial fibulectomy; Post-1day: One day after upper partial fibulectomy; Post-3months: 3 months after upper partial fibulectomy; Post-6months: 6 months after upper partial fibulectomy; Affected: Affected and operated side; Unaffected: unaffected and unoperated side; P1: Comparing Pre and Post-1day; P2: Comparing Pre and Post-6months ; P3: Comparing Pre and Control; P4: Post-6months and Control.

Means (standard deviations) are provided above for gait parameters.

Figure 3A-C. — Changing trend of muscle activity before upper partial fibulectomy and during the 6 months follow-up. (A). Biceps femoris (Caput Longum). (B). Biceps femoris (Caput Breve). (C). Peroneus longus.

Affected: operated side; Unaffected: unoperated side; m: month.

Discussion

Results from the current study provide evidence to support the feasibility and potential benefits of upper partial fibulectomy in patients with medial knee OA. This study showed that upper partial fibulectomy can immediately and greatly relieve medial knee pain and improve function within 6 months after fibulectomy. Moreover, the resulting change in KAM and muscle activity did not produce any adverse effects (assessed by one orthopedic surgeon, one physical therapist and one nurse separately, 3D gait analysis and musculoskeletal model dynamic analysis) on the lower limb over the course of the 6 months of follow-up.

On the day after upper partial fibulectomy, all patients reported greatly reduced or resolved medial knee pain, and the surgical site pain was mild. Therefore, we suspected that functional changes might be measurable immediately after the surgery. Since most of the patients could walk freely without a walking aid one day after surgery (supplemental videos are provided demonstrating the gait of the most recent 13 cases, before and one day after surgery), this time-point was included in the follow-up investigations of the biomechanical mechanisms underlying the treatment effects of upper partial fibulectomy.

Pain is the major complaint made by patients suffering from KOA and is the principal cause of disability and loss of autonomy in seniors [26, 27]. Consequently, recommended guidelines for the management of KOA focus primarily on pain relief and functional improvement [28, 29]. This study showed that pain from the medial knee was greatly relieved or even gone immediately (one day) after the upper partial fibulectomy and continuously improved during the 6 months of follow-up. The VAS pain score decreased by 96.9% compared with decreases of 42.4%, 40.4% [13], 9.0% [12] and 44.4% [11] reported for treatment with lateral wedge insoles, acupuncture, knee braces and toe-out gait modification, respectively. This finding supports the only other published report of upper partial fibulectomy for those with knee OA [17].

Partial fibulectomy also led to steady functional improvement based on HSS score and gait parameters. Importantly, the change in stance time of the two sides showed a differential response one day after surgery. In our study, the asymmetry of the gait one day after surgery was reflected in the kinematic differences comparing the two sides, such as stance time (Cycle time%) and active flexion/extension knee ROM during walking (°). We found that there were no differences between one day after and before surgery in the Z axis (vertical direction) or X axis (direction of progression) maximum ground reaction force (Supplemental Figure 1 and Table 1). The relative decreases in the ground reaction force on the affected and unaffected sides were in the Y axis (lateral direction). However, the kinetic parameter in the Y axis (lateral direction) remained stable from day one to 6 months follow up, when patients had symmetric gait. Therefore, kinematic differences between the two sides one day after partial fibulectomy did not influence the loading status of the two sides.

In our study, continuous improvement of the HKA angle was seen from day one after surgery to the 6-month follow-up assessment (no significant further change was noted between 3-month and 6-month follow-up assessments) with a mean of 1.80 degrees increase. Our findings therefore showed that a more neutral alignment was achieved for patients 6 months after upper partial fibulectomy. Two studies that used opening wedge high tibial osteotomy to treat medial compartment knee osteoarthritis reported mean increases of the HKA angle of 7.8 degrees [30] and 8.6 degrees [31] from a more varus to more neutral alignment. However, the baseline varus deformity of these subjects was 7 degrees [30] and 6.7 degrees [31], respectively, which were greater than the mean baseline varus deformity (2 degrees) in our study. Thus, the range of HKA alteration for upper partial fibulectomy (mean increase of 1.80 degrees from a more varus to more neutral alignment) is less than high tibial osteotomy (HTO). Considering that neutral HKA alignment in healthy adults is between 178.50 and 179.00 degrees [32, 33] but not a fixed target of 180 degrees usually used in surgery [30, 31], the more modest HKA change with fibulectomy led to attainment of a near normal alignment in our subjects. Therefore, the less invasive upper partial fibulectomy procedure may provide near normal HKA alignment as an alternative to the more complicated HTO procedure that requires a longer recovery time, at least in subjects with modest baseline knee malalignment. More studies would be required to determine the range of malalignment able to be corrected with fibulectomy.

KAM is generally regarded as an important proxy for medial tibiofemoral compartment loading during walking [8, 34, 35]. The overall peak KAM has been shown to be associated with clinical outcomes related to medial compartment knee OA including lower limb malalignment, medial compartment disease severity, and tibial bone mineral density ratios [11]. Our study showed a mean 11.1% reduction of overall peak KAM for the affected (operated) side. This is less than the mean decreases in KAM with medial HTO of 47.8% [36] and 57.6% [37] 6 months after surgery. This magnitude is however comparable to the magnitude of change in KAM for some other interventions: 20% reduction in response to a 6 weeks toe-in gait modification [38], 10% reduction in response to 10 weeks toe-out gait modification [11] and about 10% in response to valgus braces with a three point bending force mechanism [12]. Miyazaki et al. [39] have shown that an approximate 25% increase in overall peak magnitude of the KAM at baseline was associated with 6.6 times the risk of radiographic medial compartment disease progression over 6 years. Bennell et al. [40] showed that the total area under the KAM-time curve (KAM impulse) at baseline was predictive of loss of cartilage volume over 12 months using magnetic resonance imaging. Taken together, these findings point to an important role for quantification of the KAM in knee OA and suggest that 10–20% reduction of the overall peak KAM, as achieved in this study in response to upper partial fibulectomy, contributes to slowing of knee OA progression.

Although we do not know the precise mechanism by which upper partial fibulectomy improved HKA angle and reduced the overall peak KAM, we hypothesized that increased muscle activity of biceps femoris may be responsible. Compared with healthy controls, preoperative assessments showed that the KOA patients had significant lower muscle activity of biceps femoris for the affected (operated) side, which was in agreement with Sritharan et al. [41]. Interestingly, the muscle activity increased immediately and was equivalent to controls by 6 months after surgery. Furthermore, we noted that after surgery the proximal fibula head was displaced superiorly in 10 cases and inferiorly in 19 cases. The displacement of proximal fibula head was measured on knee joint antero-posterior radiographs (Supplemental Figure 2). This displacement may be caused by competition of muscles (Biceps femoris versus Peroneus) attached to the fibular head that creates a tension in the lateral knee that may cause the observed improvement in HKA angle from a more varus to more neutral alignment. This hypothesis may explain the continuously reduced KAM angle from one day to 6 months after surgery.

In addition, based on the known mean value of overall peak KAM (0.33 ± 0.10 Nm/kg) of 20 healthy controls (and two related studies that reported 0.40 ± 0.109 Nm/kg [42] and 0.312 ± 0.076 Nm/kg [43]), individuals outside this norm can be advised to protect the knee joint under a doctor’s guidance. We observed that the overall peak KAM of the unaffected side also decreased and assumed the same level as the affected side after surgery. This suggests that the improved medial knee loading for an affected side can contribute to improvement in the loading of the contralateral side and the balance for both sides. Further research with larger sample sizes and longer follow-up time is necessary to better understand the biomechanical and clinical benefits of upper partial fibulectomy.

The patients with medial compartment KOA are getting younger. In our study, the youngest patient was 42 years old. Since younger healthy people have better kinematic parameters (such as speed, active ROM) and normal medial compartment loading, we chose a young healthy group of individuals (mean age 27.27 ± 3.20) as the reference controls for purposes of 3D gait and musculoskeletal analyses. Comparison to this reference group in effect represents the most stringent test of the benefit of upper partial fibulectomy. In our study, we found that by 6 months after surgery, the operated knee OA patients showed gait patterns and muscle activity similar to healthy controls.

Despite the favourable outcomes found in this study, there are a number of limitations that must be taken into account and should be addressed in future studies. First, there was no sham surgical group with which to assess fibulectomy in a truly blinded and non-biased manner. Second, the sample size was relatively small, and the follow-up time was relatively short. Future research with larger sample sizes and longer follow-up times are necessary to better understand the biomechanical and clinical benefits and limitations of upper partial fibulectomy. Third, kinetic and kinematic data for the hip and ankle were not included in the gait analysis. Further study should focus on the influence of upper partial fibulectomy on adjacent joints. Fourth, in this study we only compared upper partial fibulectomy with non-invasive procedures. Some studies have observed a greater placebo effect for more invasive procedures [44]. Therefore, this study design might contribute a bias toward better outcomes in the fibulectomy treated group. In the future, we plan to compare upper partial fibulectomy with other invasive procedures such as HTO. Fifth, the anterior or posterior displacement of the fibular head could not be determined from the radiographic views obtained in this study. In future lateral views should be performed in addition to antero-posterior views to investigate displacement of the fibular head to more clearly understand the mechanism by which upper partial fibulectomy improves knee alignment and reduces medial knee loading.

In conclusion, the short-term clinical outcomes for patients with moderate radiographic knee OA in this non-randomized and uncontrolled study appear comparable or better than current treatments including lateral wedge insole, valgus knee braces, toe-out gait modification and acupuncture for patients with medial compartment knee OA. Although biomechanical evidence in this pilot study showed benefit from partial upper fibulectomy, the long-term clinical outcomes and rationale for the improvement in clinical symptoms based on change in muscle activity, correction to a more normal limb alignment and reduction in KAM should be investigated further in the future.

Supplementary Material

Supplemental Figure 1

Supplemental Figure 1. Coordinates in 3D gait analysis.

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Supplemental Table 1

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Case1_post_1day

Supplemental videos. Demonstrating the gait of the most recent 13 cases, before and one day after surgery, from February to May 2016 when our gait lab was equipped with a synchronous video camera.

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Supplemental Figure 2

Supplemental Figure 2. Measurement of vertical displacement of proximal fibular head after upper partial fibulectomy. Knee radiograph before (A) and after (B) upper partial fibulectomy. L: represents the tibial platform line; a: represents the distance (mm) between the tip of fibular head and tibial platform line before surgery; b: represents the distance (mm) between the tip of fibular head and tibial platform line after surgery. The value of (b-a) represents the vertical displacement of proximal fibular head after upper partial fibulectomy.

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Acknowledgments

We wish to acknowledge funding from National Natural Science Foundation of China under Grant (81601894), Science & Technology Foundation of Sichuan Province of China (2017HH0062) and Science and Technology Foundation of Chengdu Science and Technology Bureau (2016-GH02-00102-HZ) as well as the NIH/NIA 028716 (VBK).

Role of the funding source

The funding organizations had no involvement in the study design, collection, analysis or interpretation of data, in the writing of the manuscript, or in the decision to submit the manuscript for publication.

Footnotes

Conflict of Interest

None of the authors have competing interests to disclose. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.

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