Proximal Fibular Osteotomy for Medial Compartment Knee Osteoarthritis: Is It Worth?

Abstract

Background

Osteoarthritis of knee is one of the important causes of knee pain in elderly patients and is a debilitating disease. It often leads to varus deformity of knee. Many treatment options are available for this progressive knee joint disorder. Proximal fibular osteotomy (PFO) is a novel yet simple procedure used to alleviate the symptoms of medial compartment knee osteoarthritis. The present study was undertaken to evaluate whether this procedure improves the symptoms, functions and limb alignment in patients with medial compartment knee osteoarthritis.

Methods

Following approval by the Institutional Review Board, this prospective study included 42 cases (56 knees) with Kellgren–Lawrence grade II and III medial compartment knee osteoarthritis and underwent proximal fibular osteotomy. Clinical assessment was done by visual analogue scale (VAS) score and The Western Ontario and McMaster universities osteoarthritis Index (WOMAC) score pre-operatively and at 3, 6 and 12 months follow-up for pain and functional improvement. Radiological assessment was done by measuring femoro-tibial angles (FTA) pre-operatively and at 1 year follow-up.

Results

The mean age was 58.30 years. There were 30 females and 12 males. The preoperative mean WOMAC score was 87.3, at 3 months follow-up it was 29.4 this was significantly better (p < 0.05) but the improvement was not significant at subsequent follow-up visits. Similarly the VAS scores also showed significant improvement at 3 months, but not at 6 and 12 months follow-up. There was no significant improvement in the femoro-tibial angle (FTA) at 1 year follow-up.

Conclusion

The study highlights that both the VAS scores and WOMAC scores were significantly better at 3 months after surgery. However these did not show any significant improvement at 6 and 12 months. It does not change the alignment of knee at one year follow-up. The authors conclude that proximal fibular osteotomy provides only short-term relief in patients of medial compartment knee osteo-arthritis.

Electronic supplementary material

The online version of this article (10.1007/s43465-020-00160-0) contains supplementary material, which is available to authorized users.

Introduction

Knee osteoarthritis (OA) is a common joint disease, with an incidence of 30% in population older than 60 years [1]. The initiation and progression of knee osteoarthritis depend upon mechanical, structural, genetic, and environmental factors [2]. Knee varus deformities are common findings in patients with knee osteoarthritis and affects 74% of patients with idiopathic osteoarthritis [3]. It has been reported that even in healthy knees the medial compartment bears 60–80% of the load [4]. However, no precise document is available which states as to what contributes to this uneven load distribution. The load is distributed along the mechanical axis, which is generally medial to the centre of the knee. The various treatment modalities available for osteoarthritis knees are medications in the form of analgesics, chondroprotective drugs, intra articular injections of steroids, viscosupplementation, physical therapy, surgeries like high tibial osteotomy, arthroscopic lavage, autologous chondrocyte implantation and total knee replacement [5]. The choice of treatment depends on the severity of the disease. High tibial osteotomy is a technically complex procedure and may cause complications like neurovascular injury, iatrogenic fracture, and nonunion [6, 7]. Total knee arthroplasty is helpful in correcting lower extremity alignment, relieving pain, and improving the function markedly but it may not be the treatment of choice for younger, active patients or patients with mild to moderate osteo-arthritis [8]. A single arthroscopic debridement commonly alleviates symptoms of pain and is associated with high recurrence rates [9]. Proximal fibular osteotomy (PFO) is based on the theory of differential settlement (non-uniform settlement)—an entity which initiates knee osteoarthritis and promotes its progression [10]. The lateral part of tibial plateau is additionally supported by fibula and surrounding soft tissues whereas the medial side has the support of only medial tibial cortex. This, in addition to the fact that the medial side is subjected to more axial loading leads to non-uniform settlement and degeneration of tibial plateau [11, 12]. With the help of this logic, a proximal fibular osteotomy may be used to weaken the lateral fibular support & shift the loading force from the medial compartment to the lateral side and lead to correction of varus deformity and hence will influence the progression of the disease [13]. Till date few studies have been published assessing the role of proximal fibular osteotomy in the management of medial compartment osteoarthritis of knee. The present study was conducted to evaluate the radiographic and clinical outcomes of patients with medial compartment osteoarthritis treated by proximal fibular osteotomy (PFO). The assessment tools used were both subjective i.e. VAS score [14] and objective, i.e. WOMAC score [15] and femoro tibial angle (FTA).

Material and Methods

This prospective interventional study was conducted at our institute between January 2017 and December 2017. After getting approval from the institutional ethical and research committee (Institutional review board Approval No. TMMC/IEC/2017/46.), the study was carried out as per the declaration of Helsinki. After obtaining a written informed consent, patients were recruited from orthopaedic out-patient department. Patients, 40 years and older, with medial compartment osteoarthritis of knee falling in Grade II and Grade III of Kellgren–Lawrence classification were enrolled in our study. Participants not willing to enroll in the study, those having post-traumatic knee osteoarthritis, radiological evidence of OA in the lateral or patello- femoral compartment, inflammatory joint disease, previous operations around the knee, flexion deformity more than 15°, varus deformity > 15°, BMI > 25 were excluded. All the participants, included in the study were subjected to detailed history taking, thorough clinical examination and appropriate imaging work-up which included a full-leg standing ortho scanogram of the lower extremities. Calculation of WOMAC score, VAS score and FTA was done. All the participants were assessed for anaesthetic fitness.

Operative Procedure

In supine position under spinal/epidural anaesthesia with inflated tourniquet, the limb was prepared and draped. Head of the fibula was identified with image intensifier. A 6–8 cm longitudinal incision was made below the fibular head. We identified the intermuscular plane between soleus and peroneus. The muscles were split to reach the fibula. Site of osteotomy was identified 2.5 inches below the head of the fibula and multiple drill holes were made at the proximal and the distal level of the osteotomy. We avoided using the saw blades to prevent inadvertent injury to the common peroneal nerve. About 1.5 cm of the fibula was resected with the help of an osteotome. Bone wax was applied to the resected ends of the fibula. Closure was done. In bilateral involvement, both the limbs were operated at the same time.

Post operatively all the patients were given injectable analgesics and antibiotics along with other supportive medicines. Patients were discharged on the second day after surgery with the advice of quadriceps strengthening exercises. Weight bearing on the operative extremity was allowed as per as the tolerance limits of surgical pain. Suture removal was done on the 10th day after surgery.

Patients were called for follow up at 3, 6 and 12 months following surgery and were assessed by the same physician, who is also one of the authors, at each follow up visit.

Outcome Assessment Tools

The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score and the visual analogue scale (VAS) score were assessed before the procedure and then at each follow up visit. Pre-operative and final follow-up femorotibial angle (FTA) was also measured on the standing ortho scanogram of the lower extremities.

The WOMAC score is an objective questionnaire which assesses stiffness, pain and physical functions. There are a total of 24 questions, of these 17 are on physical functions, 5 on pain and 2 on stiffness.

Femoro-tibial Angle (FTA)

To calculate the FTA, weight bearing full-limb radiographs, including hip and tibio-talar joint were obtained with the tibial tubercle facing forward. To standardise the measurements, two transverse lines were drawn perpendicular to the shaft of tibia and femur. Anatomical axis of femur and tibia were drawn by a line connecting the midpoints of these perpendicular lines [16]. The lateral angle (FTA) was then calculated between the anatomical axes of femur and tibia.

Adverse events/complications, if any were recorded at each visit.

The sample size was calculated as 42 at 95% confidence interval, assuming the prevalence of OA knees as 39% with 2% absolute precision. A sample size was designed based on these results, with an α value of 0.05 and a power (1−β) of 0.80.

Statistical Analysis

Statistical analysis was conducted with a statistical package for social sciences (SPSS) software version 21. The outcome variable under study was VAS and WOMAC score based on categorical values, orders and ranks. Free distribution techniques have been used to analyse data. A paired analysis was performed to compare the baseline and follow-up value of the VAS and WOMAC score. Wilcoxon signed rank test (non-parametric) was used before and after the treatment to assess the important difference in the result factors. Parametric paired Student’s t test was used for comparison of quantitative data of FTA.

Results

There were total 42 patients (56 knees). The mean age was 58.30 years (range 42–65 years). There were 30 females and 12 males. 69% (n = 29) patients had K-L grade II OA knees and 31% (n = 13) had grade III OA knees. The mean WOMAC score was 87.3 pre-operatively, 29.4 at 3 months follow-up, 56.4 at 6 months follow-up and 73.4 at 12 months follow-up (Fig. 1). The mean VAS score was 8.3 pre-operatively, 2.9 at 3 months follow-up, 6.3 at 6 months follow-up and 7 at 12 months follow-up (Fig. 2). The mean preoperative FTA was 178, it was 177.30, 1 year after the surgery (Fig. 3). Though the WOMAC and VAS scores showed significant improvement at 3 months follow-up (p < 0.05), there was no statistically significant improvement in scores at 6 month (p = 0.06) and 12 month follow-up (p = 0.40). As compared to pre-operative values, there was no significant change in mean FTA, at 1-year follow-up (p = 0.48).

Fig. 1.

Shows the WOMAC score comparisons before the surgery and at subsequent follow-up

Fig. 2.

Shows the VAS comparisons before the surgery and at subsequent follow-up

Fig. 3.

Shows the difference in Femoro-Tibial angle preoperatively and after 1 year of surgery

Complication in the form of paresthesia over dorsum of foot were seen in five patients (nine extremities) which was transient and relieved in upto 5 weeks time.

Discussion

OA knees is a chronic debilitating joint disorder that leads to functional impairment and physical disability. The surgical treatment of this condition includes HTO, arthroscopic lavage, unicondylar knee arthroplasty (UKA) and total knee arthroplasty (TKA). Proximal fibular osteotomy is a new procedure that has shown promising results in medial compartment OA knees. Yazdi et al. [17] was the first to suggest that fibulectomy leads to reduction of compartmental pressure on the medial side. Many theories have been put forward to explain the rationale behind PFO. Dong et al. [18] proposed the theory of non-uniform settlement. Prakash L [19] put forward the theory of “too many cortices”, Huang et al. [20] proposed the concept of competition of muscles. Xie et al. [21] attributed the success of PFO to ground reaction vector readjustment theory. Whatever be the mechanism, most of the studies have shown symptomatic improvement in patients. Only a short term reduction in WOMAC and VAS score was seen in our research at 3 months of follow up after surgery. Follow ups at 6th month and 12 months had shown reduction in WOMAC and VAS scores compared to baseline but these were not statistically significant. Wang et al. [22] conducted a study on 47 patients with a mean age of 63.96 years. They followed up the patients for 12 months and noted that mean VAS score decreased from 8.02 pre-operatively to 2.74 at final follow-up. Majority of their patients were females (35 out of 47). They observed correction of lower limb alignment in only eight patients. Yang et al. [10], conducted a study on 156 patients with mean age of 59.2 years and follow-up of 49.1 months. At final follow-up, the mean FTA, lateral joint space and Knee Society Score (KSS) were significantly better. Four patients had numbness over the leg and six had weakness of the great toe, which was transient and became normal in 4 weeks. Zou et al. [23] conducted a prospective comparative study on PFO versus HTO and concluded that the short-term and long-term effects of PFO are better than HTO. We recruited 42 patients in our study with a mean age of 58.30 years. There was significant improvement in mean VAS score and WOMAC score 3 months following surgery, but follow-up at 6 and12 months did not show any significant improvement in these variables. Similarly we did not find a statistically significant improvement in FTA at 12 month follow-up. The present study is different from the preceding studies as we have recorded the VAS and the WOMAC scores serially at 3, 6 and 12 months follow-up, this has not been done by most of the researchers where only one final follow-up values have been compared with the preoperative values. This enabled us to ascertain the temporal change in scores at successive follow-up visits. Thus suggesting reduction in beneficial effects of the surgery with time, which has not been noted by any of the previous studies. Also, as compared to other studies, we did not see any significant changes in knee angles at 1 year follow-up.

Common peroneal nerve (CPN) palsy has been reported to be a potential complication of this surgery. Ogbumedia et al. [24] studied the risk of common peroneal nerve injury while performing HTO and found that the CPN branches at a distance of 8.2 cm below the fibular head and the maximum risk of injury to the CPN occurs within the proximal 15 cm of the fibula. Yang et al. [10] reported CPN injury in 1.8% of cases and superficial peroneal palsy in another 1.8% cases. They also reported that 14.5% cases had weakness which recovered in 4 weeks time. 11.9% patients in our study had paresthesia on the dorsum of the foot, which got relieved in 5 weeks. Though the paresthesia reported in our study is high, it was noted in most of our initial cases where we used to give smaller incisions which led to vigorous retraction and hence parasthesia. Later on we were more liberal in giving incisions. Also we did not use saw to cut the bone, for the fear of injuring the nerve by the oscillating blade in a tight space, rather we used drill and osteotome for osteotomy. Parasthesia was tackled by giving neurotropic in the form of methylcobalamin and folic acid supplements and also patient re-assurance. It recovered by the end of 5 weeks in all patients.

The limitation of the study is that there was no comparative group, we did not assess the effect of age and gender on the outcome. Also outcome evaluation could have been done for combination strategies like PFO with orthobiologics/arthroscopic interventions. Well-designed double blinded randomised controlled trials are needed to establish PFO as a modality of treating OA knees.

Conclusion

The study highlights that both the VAS scores and WOMAC scores were significantly better at 3 months after surgery. However these did not show any significant improvement at 6 and 12 months. It does not change the alignment of knee at 1 year follow-up. The authors feel that proximal fibular osteotomy provides only short-term relief in patients of medial compartment knee osteo-arthritis.

Electronic supplementary material

Below is the link to the electronic supplementary material.

Compliance with Ethical Standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical standard statement

This article does not contain any studies with human or animal subjects performed by the any of the authors.

Informed consent

For this type of study informed consent is not required.