Outcomes of medial opening wedge high tibial osteotomy following concomitant arthroscopic procedures in medial compartmental osteoarthritis of knee

Calculation of surgical correction

The patient was examined for correctability of varus deformity, range of motion (ROM), and ligament laxity. Radiographic assessment was done to know the mechanical axis and degree of correction. The amount of correction needed to achieve a normal valgus angle of 5°–8° of valgus was calculated and an additional 3°–5° of overcorrection was added

Procedure

The patients were positioned supine on the operating table. A radiolucent extension is applied to enable fluoroscopic examination. A tourniquet was applied. If a large correction is anticipated, the ipsilateral iliac crest is draped, and a rolled blanket is placed under the same buttock. A quick diagnostic arthroscopy was routinely performed to verify the status of articular cartilage and meniscus and any necessary concomitant procedure, if required like meniscal balancing, partial meniscectomy, cartilage debridement, or anterior cruciate ligament (ACL) reconstruction were performed prior to osteotomy. With the knee in a 90° flexed position, a 6–8 cm long skin incision was made running from a point anterior to the insertion of pes in a posteromedial direction. Long fibers of the superficial part of the ligament were detached from the tibia. The leg was then positioned in full extension and the knee joint was adjusted exactly into AP view under fluoroscopy. Two parallel 2.5 mm k-wire were placed aiming towards the hinge point so that k-wire ends exactly at the lateral tibial cortex. Keeping the tuberosity segment 15 mm wide a biplanar osteotomy was done. Attention was paid to completing the osteotomy cut of the hard posteromedial tibial cortex. With chisels the osteotomy was spread slowly until the desired opening angle is reached, it is confirmed by comparing weight-bearingline as per preoperative (pre-op) plan. A tomofix plate was then applied to maintain the desired valgus correction and fixed screws. The wound was closed and preventive measures were taken against thrombosis.

The patients were followed up at 6 weeks, 12 weeks, 24 weeks, and 1-year intervals. Necessary records of their functional and pain scores were documented and graded as per the Knee Society Scoring System. Also, radiological assessment of knee at above intervals with documentation of a range of tibio-femoral varus/valgus angle was done and recorded [Figures 2 and 3]. The records were maintained as per pre-tested performa appended. Data were entered in an Excel sheet and was analyzed by means of Epi info version 6.0. Paired t-tests were applied to compare preoperative (pre-op) and postoperative (post-op) measures [Table 3].

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Figure 2

(A) Tomofix plate, osteotomy chisels, bone spreader, soft lock, osteotomy gap measuring device, guidewire and drill, chisels of different sizes (B) intraoperative fluoroscopic image, (C) maintained osteotomy site and fixing with Tomofix plate, (D) clinical picture of preoperative varus and postoperative valgus

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Figure 3

(A) Mechanical axis of leg and anatomical axis of femur and tibia (B) mechanical axis passing at 15% proximal tibial articular surface (C) post-operative mechanical axis

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Ideal age for high tibial osteotomy

Insall et al.^[11] recommended that high tibial valgus osteotomy be reserved for patients younger than 60 years of age. Coventry et al.^[12] suggested that the age of the patient is irreverent for surgery and the average age of patients in the series was 49 years. Although the mean age of participants in our study was 46.9 years, which correlate with the recommended and suggested mean age in other studies, we felt that osteotomy should not be denied to patients based on the age if the other criteria like unicompartmental involvement and stable joint with no fixed deformities are present.

Pain relief

Arnoldi et al.,^[13] felt that the relief of pain was due to the lowering of the intraosseous venous pressure. Patients with degenerate OA knee have impaired venous drainage from the juxtachondral cancellous bone across the cortex. Intravenous phlebography showed that pain disappears when the high medullary pressure is released by osteotomy. Helal et al.,^[14] explained that the absence of resting pain was due to decongestion.

Coventry et al.,^[12] agreed with this hypothesis that osteotomy may lower intraosseous hypertension in the short term. The mechanical realignment of the joint with the transfer of load from the involved compartment to the opposite normal compartment is explained as the reason for the relief of pain. Here, we agree with Insall et al.,^[15] and Vainionpaa et al.^[16] that the effect of the pain relief is due to mechanical factors contributing to realignment with osteotomy.

Insall et al.,^[15] reported 97% with no pain and 3% had mild pain. In Coventry et al.,^[17] study 67% of patients had mild pain, 24% had moderate pain, and 7% had severe pain during follow-up. In our study, pain either disappeared or was relieved to a large extent after surgery. There was more pain relief in our study when compared with the Coventry et al.,^[17] study but was less when compared with the Insall et al.,^[15] study.

Tibiofemoral angle

The rationale behind the HTO is to shift the mechanical axis from the medial compartment to the lateral compartment which in turn will reduce the load on the medial compartment of the knee. The mechanical axis is formed by a line drawn from the center of the femoral head to the center of ankle. During normal single-leg stance, the medial compartment bears 75% of load due to inherent 2° of varus (tibiofemoral mechanical varus) of knee. As we shift the mechanical axis to 4° of valgus, the load on medial compartment decreases to 50%. And it decreases further to 40% when the mechanical axis reaches to 6° of valgus at knee. It is not possible to unload the medial compartment completely. So, the targeted mechanical axis is between 4° and 6° of valgus. This passes between 30% and 40% lateral to the center of the tibial spine and is known as MAD or Fujisawa point.^[11]

Insall et al.,^[15] reported that the best results were obtained in knees which had tibiofemoral angle between 10° and 14° postoperatively. They felt that postoperative valgus angle between 5° and 14° to be acceptable. Coventry et al.,^[17] recommended 5° overcorrection beyond the normal angle of 5°–8° of genu valgum, or a final tibiofemoral valgus angle of 10°–13°. Paley et al.^[18] showed that 2°–4° of mechanical valgus over correction achieved the best results whereas neutral alignment, under correction or significant over correction led to inferior results. They recommended ideal valgus angulation to be at 7°–9°. This finding suggests that there is individual variation and the question still remains is how much valgus angulation is correct amount. We found that the overcorrection should be at least 2°–4° of valgus but cannot specify an upper limit with certainty. We noted good results if an average tibiofemoral valgus angulation measured 5.96°, two rated poor knees in our series had valgus angulation <5°.

Regression of varus angle

In a study carried out by Pande et al.,^[1] modular dynamic fixator couldn't make a large number of patients comfortable and noticed significant loss of correction after removal of fixator within one year with worrying observation as maintenance of correction is the most important factor to ensure good outcome in the long term. During the follow-up period no regression in varus noted in our study. Rigid fixation helps better in maintaining the valgus in the postoperative periods. In Coventry et al.,^[17] study after five-week fall, 70% of knees showed mild regression at a rate of 1°, after five years. Insall et al.^[15] reported regression to varus deformity after 29 of 95 osteotomies that had been performed without internal fixation.

Range of motion

In our study, the mean preoperative ROM was 120.5° and postoperatively ROM knee was 128.5°. There is an increase in ROM mean of 8°. Using paired t-test, the P value was 0.001, which implies that postoperative ROM with HTO is significantly improved. None of the patients lost any further flexion in the final follow-up. In our study, patients were mobilized on the second postoperative day with partial weightbearing mobilization after teaching active quadriceps exercises. This proportional increase in ROM was probably due to early mobilization. The same can be observed from previous studies of Weidenhielm et al.,^[19] and Lawrence et al.^[20] A loss of ROM was observed in Insall et al.,^[15] and Coventry et al.,^[17] study where the patients were immobilized in plaster cast and partial weight bearing was advised from the third day and one week, respectively.

Stability

Coventry et al.,^[17] reported three cases of gross instability out of 76 knees after using his techniques of lateral collateral ligament reconstruction. Sixteen patients had mild instability in Insall's et al.,^[15] study and 10 patients had moderate instability during final follow-up. In a similar study carried out by Kyung et al.,^[21] a firm fixation using TomoFix plate for open wedge HTO produced better radiologic results and a low complication rate than those of the Aescula spacer plate. All 26 patients of our study had undergone medial opening wedge osteotomy fixed with Tomofix plate. We found the plate was extremely convenient and there was no case of instability reported. We noticed that pain and instability were closely related. We believe that by using a rigid plate (Tomofix) for fixation of osteotomy helped in achieving the stability.

Functional outcome

In our study, 53% of the cases had good, 35% had excellent, and 12% had fair functional outcomes. Preoperative mean Functional score in Knee Society Score was 41.08 and mean Functional score postoperatively at 6, 12, 24 weeks, and 1 year was 59.42, 75.96, 79.81, and 80.19, respectively. Using student's t-test, P value is 0. 001, which shows that Knee Society Score for a functional outcome is significantly better than preoperative cases. These findings correlate with the previous studies conducted by Saito et al.,^[22] Niemeyer et al.,^[23] and Bonasia et al.,^[24] which have shown significant improvement in the functional outcome after different techniques of HTO. Ultimately as per our study, the main reasons for the improved functional outcome were redistribution of loading, reducing tension on opposite stretched ligaments, reducing the impingement of degenerate meniscus on capsule, reducing capsular stretching, and tearing by correcting varus or valgus deformity and altering of blood supply specially reducing venous stasis and intramedullary pressure.

Improvement in gait

Complications

Although the complication rate in our study was less, the possible reasons for the complications usually are overcorrection or under-correction of the varus deformity, bone necrosis due to improper osteotomy technique, intra-articular fracture of the tibial plateau, an osteotomy too near the joint line will not allow placement of all screws in the proximal fragment, injury to the neurovascular bundle, and postoperative compartment syndrome. In our study, one patient (3.8%) developed an infection (SSI), which was treated with intravenous antibiotics and removal of implant after the union. One patient (3.8%) had terminally painful movement at final follow-up. There was no nonunion in our series. The bony union was rapid because the osteotomy was through cancellous metaphyseal region of the tibia. Coventry et al.,^[17] in his series of 86 knees noted no delayed or nonunion when the osteotomy was proximal to the tibial tuberosity but noted some delay in union when it was distal to the tibial tuberosity in a few cases. In our study, we didn't notice any peroneal palsy in the follow-up period.

Limitations

One of the limitations of our study was that we did only medial opening wedge HTO, while we could not compare it with lateral closing wedge osteotomy, which would otherwise give a better comparison. Second, medium-term follow-up for all cases was not possible due to the constraint of time.

Financial support and sponsorship

Nil.