Comparative study of medial opening wedge high tibial osteotomy using fixator-cum-distractor device or locking plate in medial unicompartmental osteoarthritis of knee

Abstract

Objective

The aim of our study was to evaluate the role of medial opening wedge high tibial osteotomy (MOWHTO) in medial unicompartmental osteoarthritis of the knee and compare two different fixation devices for stability, duration, outcome, and complications.

Methods

Fifty-seven patients (60 knees) of age < 60 yrs and either sex with medial unicompartmental osteoarthritis of the knee were divided into 2 groups. Twenty-four patients (25 knees) in Group I underwent MOWHTO using fixator-cum-distractor and 33 patients (35 knees) in Group II underwent MOWHTO using locking plate osteosynthesis. The results were assessed by VAS, KOOS and WOMAC score.

Results

Mean age of the patients in Group I was 53.13 ± 5.20 years and 51.32 ± 6.91 years in Group II. Mean preoperative varus deviation was 11.97 ± 3.34° in Group I and 11.78 ± 3.05° in Group II which was corrected to 3.27 ± 1.75° and 3.56 ± 1.47° valgus respectively. All the patients achieved full weight bearing by 35th day postoperatively in Group I with the mean of 30.27 ± 2.71 days and 38th day in Group II with the mean of 30.32 ± 3.08. The VAS, KOOS, and WOMAC score improved significantly postoperatively in both the groups.

Conclusion

The difference between the two methods of fixation was statistically insignificant. Fixator-cum-distractor is minimally invasive giving good control over the final limb alignment; however, it is cumbersome with less patient compliance and has complications like pin tract infection. Locking plate provides better fixation stability than fixator-cum-distractor even without bone grafting; however, it is an invasive procedure requiring more soft tissue exposure and precise amount of wedge removal.

1. Introduction

Medial unicompartmental osteoarthritis of the knee (MCOA) accounts for more than one-third cases, probably due to more stresses on the medial compartment of the knee during one-legged stance.¹ Studies in the literature show an important role of Medial opening wedge high tibial osteotomy (MOWHTO) in the treatment of MCOA and symptomatic varus malaligned knees.^2,3 Efficacy has been demonstrated in the short, medium and long term by reducing, or even eliminating, the pain by unloading the medial compartment.⁴ An ideal patient for HTO is a young, active patient <60 years of age, mild to moderately symptomatic varus knee with medial unicompartmental involvement, >90° knee range of motion (ROM), without any ligamentous laxity or instability.⁵

Various studies describe numerous methods of fixation, such as staples, plate and screws, and a unilateral external fixation system.⁶ Standard fixator devices using minimally invasive approaches minimize complications from more extensive soft tissue exposures. The availability of locking plate with locking screws makes the construct more stable and reliable protecting the osteotomy site with a defect, till the body naturally replaces the lost bone.⁷ In this study we compare two different systems of fixation for MOWHTO and assess the stability of these fixation devices, duration of treatment, the incidence of complications, and the final alignment they produce by using visual analogue scale (VAS)/Knee injury and osteoarthritis outcome score (KOOS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score.

2. Material and methods

We prospectively reviewed a total of fifty-seven (57) patients with sixty (60) knees of either sex divided randomly into two groups i.e. Group I & Group II, with approval from the EC committee. Inclusion criteria included cases with (i) medial unicompartmental involvement, (ii) age < 60 years, (iii) body mass index (BMI) of <30, (iv) deformity correction <20°, (v) ROM knee >90°, and (vi) no ligament instability. A total of 24 patients (25 knees) were included in Group I and was treated with MOWHTO using a Fixator-cum-distractor device. Out of 24 patients, in 18 patients we used turnbuckle (hexagonal) type of fixator distractor device. Designed and fabricated in our Orthopedics workshop and in rest of 6 patients, we used railroad type of fixator distractor device (dynamic axial fixator). Another, 33 patients (35 knees) were included in Group II and were treated with MOWHTO using locking titanium plate osteosynthesis (DePuy Synthes, TomoFix Osteotomy System). Initially, the group allocation was based on randomization but, due to financial implications, the group allocation was made according to the patient's choice of implant.

Detailed history regarding age, weight, height, BMI, occupation, activity level, previous surgeries, co-morbidities, and the pain was noted. Clinical knee examination was done using parameters of per VAS,⁸ KOOS⁹ and WOMAC¹⁰ score. All knees were graded according to the severity using the Kellgren Lawrence grading system.¹¹

Standing anteroposterior (AP), lateral x-rays of both knee joints and scanogram from bilateral hips to ankles in weight-bearing position were done to note the anatomical axis, mechanical axis, and weight-bearing line. Fujisawa et al.¹,¹² technique was used to evaluate the correction angle and the amount of opening of the osteotomy gap.

2.1. HTO with locking plate osteosynthesis technique

Under spinal anesthesia, the patient was placed in the supine position with a pneumatic tourniquet on the affected limb. A 5 cm long incision was given medially between the tibial tuberosity and the posteromedial condyle of the tibia. The pes anserinus was dissected and detached from its tibial insertion to expose the medial collateral ligament. The distal portion of this ligament is lifted off using a periosteum elevator and a blunt lever is placed posteriorly to protect the neurovascular bundle. Under fluoroscopy, two guide wires were inserted medially 4 cm below the joint line and directed obliquely towards the head of the fibula. An osteotomy was performed along the guide wires using an oscillating saw and an osteotome. The osteotomy extends from the tibial tuberosity along the posteromedial condyle of tibia, parallel to the tibial slope without damaging the hinge of lateral cortex towards the apex of angulation. The mobility at the osteotomy site was confirmed and using stacked osteotomes a valgus force was applied to open the osteotomy site which also reduces the risk of tibial plateau fracture. A calibrated wedge was then inserted until the osteotomy site opened to the desired extent. Once the desired amount of correction was achieved, internal fixation with a locking plate was done (Fig. 1).

Fig. 1.

Showing intra-operative fluoroscopy images and clinical picture of medial opening wedge osteotomy & internal fixation with locking plate.

2.2. HTO with fixator-cum-distractor technique

Under spinal anesthesia, the patient was placed in the supine position with a pneumatic tourniquet on the affected limb. Under fluoroscopy, a Schanz pin was passed through a T-piece hole beneath the subchondral bone of tibial condyles, and 2 more Schanz pins through the fixator clamps in the tibial diaphysis. In 11 patients we used railroad type of fixator distractor device (dynamic axial fixator) and in 14 patients we used turnbuckle (hexagonal) type of fixator distractor device. Another Schanz pin was passed through the T-piece hole parallel to the first pin in the tibial condyles such that they overlapped each other in the AP view. The fixator was then detached and an incision was given from the joint line to the tibial tuberosity. The incision was deepened to the periosteum, lifted off using the elevator and curved levers was placed to protect the medial collateral ligament and patellar tendon. The osteotomy was performed between the juxta-articular Schanz screws and the tibial tuberosity. The osteotomy line extends from the tibial tuberosity along the posteromedial condyle of tibia, parallel to the tibial slope without damaging the hinge of lateral cortex towards the apex of angulation. Mobility at the osteotomy site was checked for its completion. The wound was closed in layers. Fixator-cum-distractor was assembled to the Schanz screws (Fig. 2). The gradual distraction of the callus was started from a 5th postoperative day at a rate of 1 mm/day (divided in 2 times/day) till the desired correction. After achieving normal limb alignment, the fixator was kept in place till consolidation. Distraction process and pin track cleaning and dressings was taught to the patients and was done by themselves at home.

Fig. 2.

Showing intra-operative fluoroscopy images of HTO with Schanz screw insertion assembled with Fixator-cum-distractor.

All the patients of both groups were followed up to six months. Initially, at 2 weeks interval for the first one month and then at monthly interval till six months. Bony union was assessed by radiographs on a monthly basis. The full-length radiograph (scanogram) at the sixth month showing bony union and maintenance of correction was their endpoint. Complications, if any, were noted and managed accordingly. The results were assessed by VAS, KOOS and WOMAC score and analyzed using student t-test. A p value of <0.05 was considered significant. However, there is a follow up of eleven patients from Group I and sixteen patients from Group II at one year and all the patients are asymptomatic and still maintaining the correct alignment. There were two dropouts from Group I and one from Group II. All three patients were excluded from the study.

3. Results

The mean age of the patients for Group I was 53.13 ± 5.20 years (range 42–60 years) and 51.32 ± 6.91 years (range 35–60 years) for Group II; with 11 males and 14 females in Group I, and 12 males and 23 females in Group II. Mean preoperative varus deviation was 11.97 ± 3.34° in Group I and 11.78 ± 2.94° in Group II. Knee ROM in Group I pre-operatively and post-operatively was 121.67 ± 8.79 and 121.33 ± 10.43 respectively. Knee ROM in Group II pre-operatively and post-operatively was 124.0 ± 9.35 and 124.45 ± 9.35 respectively. The difference in knee ROM pre-operatively and postoperatively was not significant in both the groups (p > 0.05). Moreover, the difference in ROM knee post-operatively between the two groups was also statistically insignificant (p = 0.42).

Mean observed partial weight bearing in Group I was 14.66 ± 1.63 days and 14.44 ± 1.67 days in Group II. Full weight-bearing was allowed on average in 30.27 ± 2.71 days in Group I and 30.32 ± 3.08 days in Group II. Mean observed fixator-distractor device removal time was 13.4 ± 3.29 weeks. The average consolidation time in Group I was 16.47 ± 1.68 weeks and 15.2 ± 1.44 weeks in Group II.

Mean VAS score in Group I pre-operatively and post-operatively was 6.74 ± 0.79 and 1.74 ± 0.70, and in Group II 6.6 ± 0.58 and 1.4 ± 0.50 respectively. The difference in improvement in VAS score post-operatively between the two groups was statistically insignificant (p = 0.12).

Mean walking distance improved significantly to 1143 ± 192.60 m postoperatively from 546.67 ± 134.25 m preoperatively in Group I and from 564 ± 131.90 to 1290 ± 287.59 m in Group II (p < 0.001). However, a statistical difference in post-operative walking distance between the two groups was insignificant (p = 0.06). Total, Average and WOMAC Index score preoperatively and postoperatively improved with significant difference (p < 0.001) in Group 1 and Group 2. (Table 1) However, on comparing both the groups the difference was statistically insignificant (p > 0.05).

Table 1.

showing Total, Average and WOMAC Index score preoperatively and postoperatively between the two groups.

Parameter	Pre-op	Post-op	Statistical significance		Statistical significanceGroup I & II Postoperative
Total WOMAC score	Group I	71.8 ± 4.64	19 ± 5.21	<0.001	0.82
	Group II	69 ± 8.44	17.1 ± 3.47	<0.001
Total WOMAC average	Group I	3.18 ± 0.21	0.84 ± 0.24	<0.001	0.51
	Group II	3.02 ± 0.39	0.75 ± 0.13	<0.001
WOMAC Index	Group I	79.47 ± 5.43	21.08 ± 6.10	<0.001	0.63
	Group II	75.4 ± 9.92	18.6 ± 3.47	<0.001

The total KOOS score improved significantly from 118.5 ± 3.77 to 39.53 ± 4.94 in Group I and from 114 ± 9.41 to 36.8 ± 7.27 in Group II (p=<0.001). The total KOOS index also improved significantly from 143 ± 11.7 to 366.2 ± 14.17 in Group I and from 156 ± 24.03 to 375.38 ± 29.69 in Group II (p=<0.001). On comparing post-operative KOOS score and index of both the groups, the difference was statistically insignificant (p=>0.05) (Fig. 3, Fig. 4).

Fig. 3.

Showing pre-op and post-op X-rays of locking plate osteosynthesis at 2 weeks and 6 months.

Fig. 4.

Showing pre-op and post-op X-rays of fixator-cum-distractor at 2 weeks and 6 months.

We observed pin tract infection affecting 6 patients in Group I which subsided with pin tract care and oral antibiotics in all but 2 patients in whom varus collapse was observed at 6 weeks. The fixator was removed for these 2 patients and above knee cast was given. On final follow up, both these patients had lost their valgus angulation. Two patients in Group II developed infection; one in muscular planes which were drained, while other patient had a superficial infection which healed spontaneously with oral antibiotics.

4. Discussion

MOWHTO is a common surgical technique for the management of MCOA of knee and correction of tibial mal-alignment. MOWHTO minimizes the risk of neurovascular injury and the need for wide dissection of soft tissues. The major advantage of this surgery is that it allows the unlimited activity to the patient. Patients requiring a vigorous activity for their daily routine work or who wish to continue playing sports, this osteotomy is a reasonable procedure which delays a later total knee arthroplasty.¹³ We aim to compare two surgical techniques in MOWHTO and assess the stability, duration, outcome and complications.

The mean age of the patients in our study was 53.13 years (range 35–60 years) which was comparable to the studies reported in the literature.14, 15, 16 High incidence of females in our study indicates that knee OA affected females more commonly than males. However, some studies were in contrast which had a higher number of male patients in their study.^14,15

In our study, all patients were of Grade 2 and 3 as classified by Kellgren Lawrence classification.¹¹ This was in contrast to some other studies who reported less of grade III and more of grade I & II patients in their study.^1,16,17 BMI of the patients in our study was comparable to similar studies mentioned in the literature.^1,15,17 In the present study, mean BMI was 28.23 in Group I and 27.91 in Group II.

Statistically, significant improvement was observed in the VAS score in our study from 6.74 to 1.74 in Group I and 6.6 to 1.4 in Group II. The score was maintained until the last follow-up and comparable to other study groups.^1,17

Mean observed preoperative varus deviation was 11.97 ± 3.27 in Group I and 11.78 ± 3.56 in Group II. Varus deformity in our study showed significant improvement in postoperative valgus angulation with a mean value of 3.26° in Group I and 3.56° in Group II which was comparable to other study groups in literature.^17,18

Mean observed consolidation time of osteotomy site in Group I was 16.47 weeks and 15.2 weeks in Group II. Two patients in Group I developed pin site infection with varus collapse, for whom fixator was removed at 6 weeks and long leg cast was given. Delayed consolidation (19 & 20 weeks) was reported in those patients. The mean observed time for removal of the fixator-cum-distractor device in Group I was 13.4 weeks and was comparable to some other study groups.^1,16

Significant improvement in knee pain, stiffness, and global functions were observed in WOMAC score assessment. In our study, significant improvement was observed in pain from baseline to 6 months follow up in both groups. There was a statistically significant improvement with a p-value of <0.001. In a similar manner, stiffness and global function subscales showed significant improvement respectively at 6 months follow up in both the groups. However, differences in improvement in WOMAC score on comparing the two groups were statistically insignificant with p > 0.05 for total and average WOMAC score & WOMAC index.

As seen with the WOMAC score, significant improvement was also observed in KOOS score assessment in the present study with p-value <0.001 in both the groups postoperatively. The difference in KOOS score and index on comparing the two groups using student unpaired t-test showed insignificant results (p > 0.05).

Superficial wound infection, pin tract infection, infected implant, varus collapse, delayed union, deep vein thrombosis, per-operative or post-operative lateral tibial plateau fracture, etc. are some of the frequent complications reported.^16,17,19 We found pin tract infection to be the most frequent complication in the fixator group and post-operative leg swelling in the plating group.

5. Conclusion

Correction of MCOA or varus deformity of the knee can be effectively achieved by MOWHTO by using either a locking plate or fixator-cum-distractor. Significant improvement was noted in both the groups which were assessed by VAS score, KOOS score, WOMAC score, post-operative valgus angle, and walking distance. On comparing the postoperative clinical and radiographic parameters in both the procedures we concluded that there was not much significant difference between the two groups.

Fixator-cum-distractor is less invasive with precise control over final limb alignment. It allows later fine adjustments in correction post-operatively so that perfect mechanical axis can be restored. Locking plate with locked screws provides a stable construct without filling the defect and allows early weight bearing.

Both procedures have their advantages and disadvantages. Pin site infection was the most common complication with a fixator and it was cumbersome to patients and had less patient compliance; while locking plate is an invasive procedure and requires more soft tissue exposure and precise wedge removal. It doesn't allow any residual correction post-operatively. However, the choice of the procedure depends on the patient's profile and demand, and the surgeon's preference and experience.

Conflicts of interest

The authors have no conflict of interest and nothing to declare. Moreover, there is no funding source.