The study design is a randomized controlled trial. Patients will be allocated to two groups: HTO with CWO technique or HTO with LCW technique. The study will be conducted at the Orthopedic Department of Martini Hospital in Groningen. The study design, procedures, protocols and informed consent are approved by the local Medical Ethical Committee. The trial is registered in the Netherlands Trial Registry (NTR3898).
Patients visiting the outpatient clinic of the Orthopedic Department who have an indication to undergo HTO because of osteoarthritis of the medial compartment of the knee with varus alignment will be included if they meet the following criteria: radiologically confirmed medial compartment osteoarthritis, medial joint pain, 6-12° varus alignment and age 18 and older. Exclusion criteria are: symptomatic osteoarthritis of the lateral compartment, rheumatoid arthritis, range of motion of the knee joint under 100°, flexion contracture more than 10°, grade 3 collateral laxity (Insall), history of fracture or previous open operation of the lower extremity, mental incapacity, or inability to fill in the questionnaires in Dutch.
After randomization patients will undergo either a CWO HTO or a LCW HTO; all patients will be operated on by one of two orthopedic surgeons, both experienced in applying the two techniques so there will be no bias. Preoperative the wedge-correction is calculated aiming on 4° overcorrection.
Combined wedge osteotomy (CWO)
For the combined wedge HTO, instrumentation of Allopro (Zimmer; Winterthur, Switzerland) will be used. The common peroneal nerve will be exposed and snared with a nerve band. Next, the anterior part of the proximal fibular head (anterior part of the proximal tibiofibular syndesmosis) will be resected. The proximal osteotomy is performed using an oscillating saw up to the center of the tibial head, 2 cm distally from the joint line. After positioning the aiming device in the first osteotomy, a second distal osteotomy is made, which results in a laterally-based bone wedge. The bone wedge is removed. The distal part of the tibia is placed in valgus position, so the lateral part of the osteotomy closes and the medial part of the osteotomy opens. The center of the valgisation is the center of the tibial head. The half bone wedge is placed back in the gap opened on the medial side. The osteotomy is secured with staples, two on the lateral side and one on the medial side. At the end of the procedure a fasciotomy of the anterior compartment will be performed to prevent compartment syndrome.
Lateral closing wedge osteotomy (LCW)
For the lateral closing wedge HTO, instrumentation of Allopro (Zimmer; Winterthur, Switzerland) will be used. The common peroneal nerve will be exposed and snared with a nerve band. Next, the anterior part of the proximal fibular head (anterior part of the proximal tibiofibular syndesmosis) will be resected. The osteotomy will be made and the wedge taken out. The osteotomy will be fixated with two staples. At the end of the procedure a fasciotomy of the anterior compartment will be performed to prevent compartment syndrome.
The postoperative treatment for both HTO techniques consists of a pressure bandage for 24 hours and cast immobilization until removal of the stitches, followed by flexion-extension brace protection and 50% weight bearing for 6 weeks. After this period, weight bearing can be built up to 100% based on the pain sensation of the patient, brace use can be reduced to no brace, and physical therapy will be started.
Main study parameter/endpoint
Primary outcome measure is the accuracy and preservation correction of the technique, defined by achievement of an overcorrection of 4° valgus one year after surgery as measured by the hip-knee-ankle (HKA) angle. The continuous differences in achievement of a valgus overcorrection and the deviation from 4° valgus will be determined, as well as dichotomous outcome and achievement of a 0-6° valgus alignment .
Secondary study parameters/endpoints
Secondary outcome measures are anatomical changes due to HTO and pain and function scores. Parameters are tibial slope (Moore-Harvey and Dejour-Bonin); patellar height (Insall-Salvati and Caton Index) and difference in leg length (cm) one year after surgery; and pain severity (VAS; range 0–10), knee function and quality of life (KOOS), and walking distance (km) at six weeks, three months, six months and one year after surgery.
Other study parameters
Potential confounding parameters, such as opposite cortex fractures, demographic data, length, weight and BMI will be recorded. Adverse events like re-operations, including hardware removal, will also be recorded.
Randomization, blinding and treatment allocation
For randomization a restricted randomization/blocked randomization (2×10 patients in one block) method will be used. The same number of patients will be allocated to each surgical treatment group. Two random allocation sets (for the CWO and the LCW) will be generated by a computer. These allocations are then sealed in consecutively numbered opaque envelopes. Once the patient has given consent to be included in the trial, the HTO technique (CWO or LCW) is randomly assigned by opening the next sealed envelope.
Preoperatively as well as six weeks, six months and one year postoperatively, patients will visit the outpatient clinic. Routine physical examination will be performed by the orthopedic surgeon.
Primary outcome measure–achievement of an overcorrection of 4° valgus alignment / hip-knee-ankle angle (HKA, in degrees)–will be measured after one year on a whole-leg radiograph (WLR) standing on one leg. The continuous differences in achievement of a valgus overcorrection and the deviation from 4° valgus are determined. A dichotomous outcome is achievement of a 2-6° valgus alignment.
Secondary outcome measures, posterior tibial slope (Moore-Harvey and Dejour-Bonin), patellar height (Insall-Salvati and Caton Index) and difference in leg length (cm) one year after surgery will be obtained. Pain severity (VAS; range 0–10), knee function and quality of life (KOOS), and walking distance (km) six weeks, three months, six months and one year after surgery will also be obtained.
Sample size calculation
The sample size was calculated based on an expected increase of the success rate from 60% in the closed wedge HTO to 85% in the combined wedge HTO. A successful operative result is defined as achievement of a 2-6° valgus alignment. To detect such a difference with α= 0.05 and a power of 80%, we need to include 50 patients in each study group. To adjust for possible loss to follow-up, a total of 110 patients will be included in the study.
All data will be analyzed according to an intention-to-treat principle, implying that all patients who are randomized will be included in the analyses, and that they will be analyzed according to the group to which they were allocated. For those patients who will be lost to follow-up or will be re-operated during follow-up, the last available measurement or the last measurement will be forwarded (Last Value Carried Forward technique).
A multivariable linear regression method will be used to analyze the impact of LCW versus CWO HTO on postoperative alignment, posterior tibial slope, patellar height, leg length, VAS, KOOS, walking distance and patients with adverse events at the one-year follow-up. A multivariable logistic regression method will be used for the dichotomous outcome measures. Gender, age and baseline values for HKA angle, VAS knee, KOOS, walking distance, medial osteoarthritis more than joint space loss alone, and concurrent OA of the lateral compartment will be considered as possible confounders and are included in the regression models only if they change the relationship between dependent variable and type of HTO by at least 10%. The SPSS program will be used for the statistical analyses and a p-value of 0.05 is considered statistically significant.