Opening Wedge High Tibial Osteotomy for Symptomatic Hyperextension-Varus Thrust

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1 Opening Wedge High Tibial Osteotomy for Symptomatic Hyperextension-Varus Thrust Douglas D.R. Naudie,* MD, FRCSC, Annunziato Amendola, MD, FRCSC, and Peter J. Fowler, MD, FRCSC From the Division of Orthopaedic Surgery, London Health Sciences Centre, University Campus, Fowler Kennedy Sport Medicine Clinic, University of Western Ontario, London, Ontario, Canada Background: The purpose of this study was to assess the functional outcome of opening wedge high tibial osteotomy (HTO) in a young, active group of patients with instability rather than osteoarthritis. Methods: The results of 17 opening wedge HTOs in 16 patients with a symptomatic hyperextension-varus thrust were evaluated. Functional results were evaluated according to the activity scoring system of Tegner and Lysholm and using a 5-point visual analogue scale to assess change in knee stability and satisfaction. Radiographs were analyzed to determine changes in femorotibial and mechanical axis alignment, tibial slope, and patellar height. Results: Patients were followed for a mean of 56 months. All patients had an increase in their activity score postoperatively. Nine patients rated their symptoms as significantly better and seven as somewhat better. All but one were satisfied with the surgery. Femorotibial axis alignment was changed to a mean of 6 valgus, mechanical axis alignment was corrected to a mean of 46% toward the lateral compartment, posterior tibial slope was increased a mean of 8, and the ratio of patellar height was decreased a mean of Conclusion: Opening wedge HTO can produce good functional and radiographic results in selected patients with a symptomatic thrust. Keywords: osteotomy; proximal tibia; knee; instability; thrust High tibial osteotomy (HTO) is a surgical procedure that involves cutting the proximal tibia in an attempt to change the mechanical weightbearing axis and alter the loads carried through the knee. The conventional indications for a valgus-producing HTO are the presence of medial compartment osteoarthritis and a varus malalignment of the knee causing pain and functional limitations. Both lateral closing wedge and medial opening wedge techniques have been described for these indications and shown to produce satisfactory clinical results in the short and long term. 6,13,14,22,23 Traditionally, knee instability associated with a varus thrust has been considered a contraindication to HTO because it has been associated with less satisfactory clinical results. 6,23 The indications for HTO have since expanded, however, to include patients with chronic ligament deficiencies and malalignment. 8,16,25,27 In contrast to the * Address correspondence and reprint requests to Peter J. Fowler, MD, Fowler Kennedy Sport Medicine Clinic, 3M Centre, University of Western Ontario, London, Ontario, Canada N6A 3K7. The American Journal of Sports Medicine, Vol. 32, No. 1 DOI: / American Orthopaedic Society for Sports Medicine literature evaluating the use of HTO for osteoarthritis, there is little information on the functional outcome of patients undergoing osteotomy for instability in which osteoarthritis is not the primary problem. 2,11,12,30 Our experience with soft-tissue procedures alone for the treatment of knee instability associated with varus malalignment has not been satisfactory. It has been our experience that uncorrected alignment leads to repetitive stresses and failure of the surgically reconstructed structures. We have previously reported good functional results in a small group of patients using the lateral closing wedge osteotomy alone for chronic anterior cruciate ligament (ACL) instability and varus malalignment. 11 We have used the opening wedge osteotomy to treat several patients with symptomatic posterolateral instability and a hyperextension-varus thrust. The purpose of this study was to describe and assess the functional and radiographic outcome of our operative technique. MATERIALS AND METHODS The results of 17 opening wedge HTOs in 16 patients performed by two surgeons at the Fowler Kennedy Sport Medicine Clinic in London, Ontario, Canada, between May 60

2 Vol. 32, No. 1, 2004 Symptomatic Hyperextension-Varus Thrust 61 Figure 1. Clinical photograph of a 26-year-old female (case 17) with capsuloligamentous laxity and a symptomatic hyperextension-varus thrust of her right knee and May 2000 were retrospectively evaluated. This cohort was part of a group of 103 patients who underwent an opening wedge HTO during that time. From this group, only those patients with a primary diagnosis of posterolateral instability with a symptomatic hyperextension-varus thrust were included in the study (Fig. 1). Patients with a primary diagnosis of medial compartment osteoarthritis, anterior instability, or who had been treated with combined osteotomy and ACL reconstruction were excluded. Two patients who underwent opening wedge osteotomy for this indication were lost to follow-up prior to 2 years and excluded from this study. Another patient who underwent medial opening wedge osteotomy in conjunction with meniscal allograft transplantation was also excluded. The study group therefore included 16 patients, of which there were 10 males and 6 females (Table 1). The mean age of the patients at the time of surgery was 27 years (range, 14 to 41 years). The right side was operated on in 6 patients, the left side in 9 patients, and 1 patient had bilateral surgery. The etiology of the instability was an isolated PCL injury in 4 patients, a combined PCL and posterolateral ligament injury in 7 patients, and capsuloligamentous laxity in 5 patients (Fig. 2). All patients had a history of previous trauma to the affected knee, 5 of which were involved in high-energy motor vehicle accidents. Eleven patients had previous surgery to the affected knee. Six patients had previous ligament repair or reconstruction. One patient (case 4) sustained a remote isolated PCL injury and was initially recommended to undergo HTO prior to PCL reconstruction at our institution but elected to proceed with PCL reconstruction prior to osteotomy. A second patient (case 6) sustained a combined PCL and posterolateral ligament injury and underwent posterolateral ligament repair at another institution prior to referral to our clinic. A third patient (case 8) sustained a combined ACL and PCL injury and underwent ligament reconstruction at another institution prior to presentation. A fourth patient (case 9) sustained a knee dislocation and underwent ACL and PCL reconstruction and posterolateral ligament repair at another institution prior to referral to us with residual instability. A fifth patient (case 10) had a previous ACL reconstruction and posterolateral ligament repair at another institution prior to referral. A sixth patient (case 12) with significant capsuloligamentous laxity of her knee (and multidirectional instability of both shoulders) had previously undergone ACL reconstruction, biceps tenodesis, and a tibial tubercle osteotomy at another institution prior to presentation to our clinic with residual instability. Five patients had previous arthroscopic surgery on the affected knee. The indication for osteotomy was functional disability secondary to a symptomatic hyperextension-varus thrust that had failed to respond to previous treatment, including bracing. Knee instability was confirmed clinically by the presence of posterior or posterolateral ligamentous laxity and a hyperextension-varus thrust. The highest level of activity for all patients was determined prior to undergoing osteotomy. The functional results were evaluated according to the scoring system of Tegner and Lysholm, 29 in which the level of performance in manual labour and recreational sports activities is rated on a scale from 0 points (complete disability) to 10 points (the ability to perform at the level of an elite professional athlete). Standard full-length standing anteroposterior and lateral radiographs were available for review for all patients preoperatively. The radiographic grading system for osteoarthritis of the knee described by Koshino and Machida 15 was employed in this study. The femorotibial (anatomical) axis alignment described by Moreland et al. 20 was measured on standing full-length hip-to-ankles extremity radiographs. The percentage change in mechanical axis alignment was determined using the method of Dugdale et al. 10 The posterior tibial slope was measured according to the technique of Dejour et al. 7-9 The ratio of patellar height was measured using the technique described by Blackburne and Peel. 3 This method eliminates the need for identification of the tibial tubercle and eliminates the variable patellar length by taking the articular surface length only. Operative Technique Preoperative Planning. Our evaluation begins with assessment of the extent of knee arthrosis and lower extremity alignment with bilateral weightbearing antero-

3 62 Naudie et al. The American Journal of Sports Medicine TABLE 1 Clinical Data for All Patients Who Underwent Opening Wedge High Tibial Osteotomy a Demographic Data Age Etiology of Previous Osteotomy Concurrent Follow-up Case Gender (years) Side instability Surgeries (mm) Fixation procedures (months) 1 Male 39 Right Isolated PCL Scope 10 ICBG Scope 81 2 Male 18 Right Isolated PCL 7.5 Plate 46 3 Male 41 Left Isolated PCL Scope 10 ICBG; plate 47 4 Female 30 Right Isolated PCL PCL 10 Plate 41 5 Male 23 Left PCL/PLC Scope 10 ICBG; plate Scope 44 6 Female 20 Left PCL/PLC PLC 7.5 ICBG 59 7 Female 19 Left PCL/PLC 7.5 Plate 36 8 Male 35 Left ACL/PCL ACL, PCL 5 Plate Scope 54 9 Female 14 Right ACL/PCL/PLC ACL, PCL, PLC 7.5 Plate Scope Male 23 Left ACL/PCL/PLC ACL, PLC 10 ICBG Male 21 Left ACL/PCL/PLC 12.5 ICBG; plate Female 38 Right Capsuloligamentous ACL, PLC, TTO 7.5 Plate Male 28 Left Capsuloligamentous 10 ICBG; plate TTO Male 33 Left Capsuloligamentous Scope 10 ICBG; plate TTO Male 22 Right Capsuloligamentous Scope 20 ICBG TTO Male 26 Left Scope 10 ICBG; plate 61 ICBG; plate 17 Female 26 Right Capsuloligamentous Mean Range (14 41) (5 20) (21 83) a PCL = posterior cruciate ligament; PLC = posterolateral complex; ACL = anterior cruciate ligament; ICBG = iliac crest bone graft; TTO = tibial tubercle osteotomy. TABLE 2 Functional Outcome of All Patients 29, a Preoperative Postoperative Activity Activity Stability Have it score score improved Satisfaction again? Complications Further surgeries 3 5 Significantly Yes Yes PCL 6 7 Significantly Yes Yes 3 4 Significantly Yes Yes Delayed union 0 1 Somewhat Yes Yes 4 9 Significantly Yes Yes 4 6 Significantly Yes Yes PCL, PLC; Removal HW 4 6 Significantly Yes Yes 3 4 Somewhat Yes Yes PCL 4 7 Significantly Yes Yes 4 5 Significantly Yes Yes PCL 4 6 Somewhat Yes Yes ACL, PCL 2 3 Somewhat Yes Yes 0 4 Somewhat No No Displaced TTO Revision TTO 5 6 Significantly Yes Yes 3 7 Somewhat Yes Yes Removal HW 3 4 Somewhat Yes Yes Removal HW (0 7) (1 9) a PCL = posterior cruciate ligament; PLC = posterolateral complex; HW = hardware; ACL = anterior cruciate ligament; TTO = tibial tubercle osteotomy.

4 Vol. 32, No. 1, 2004 Symptomatic Hyperextension-Varus Thrust 63 A C B D E F Figure 2. (A) Preoperative MRI of a 19-year-old female (case 7) who sustained a combined PCL and posterolateral ligament injury to her left knee demonstrating injury to the PCL. (B) Preoperative weightbearing tunnel radiograph of the same patient demonstrating absence of osteoarthritis. (C) Preoperative lateral radiograph of the same patient. (D) Preoper-ative single-leg weightbearing anteroposterior radiograph of the same patient demonstrating a weightbearing line that passes through the medial compartment of the knee (31% of the width of the tibial plateau). (E) Postoper-ative anteroposterior radiograph of the same patient after a 7.5-mm anteromedial opening wedge osteotomy fixed with a two-hole osteotomy plate (Arthrex, Naples, Florida). (F) Postoperative lateral radiograph of the same patient demonstrating an increase in the posterior tibial slope.

5 64 Naudie et al. The American Journal of Sports Medicine A B Figure 3. (A) Preoperative single-leg weightbearing anteroposterior radiograph of a 38-year-old female (case 12) demonstrating the hyperextension-varus thrust and a weightbearing line that passes through the medial compartment of the knee (9% of the width of the tibial plateau). (B) Postoperative single-leg weightbearing anteroposterior radiograph of the same patient after a 7.5- mm anteromedial opening wedge osteotomy fixed with a two-hole osteotomy plate (Arthrex, Naples, Florida) demonstrating a shift of the weightbearing line to pass through the center of the knee joint (49% of the width of the tibial plateau). posterior views in full extension, bilateral weightbearing posteroanterior tunnel views in 30 of flexion, and lateral and skyline views. 5 A single-leg weightbearing anteroposterior view is also obtained, and the required correction is calculated according to the method described by Dugdale et al. 10 The osteotomy is planned so that it will place the weightbearing line (center of the femoral head to center of the tibiotalar joint) to fall at a selected position approximately 50% across the width of the tibial plateau from medial to lateral (Fig. 3). This is in contrast to when we perform an osteotomy for osteoarthritis of the medial compartment, in which case we plan the osteotomy so that the weightbearing line will fall at a selected position 62.5% across the width of the tibial plateau from medial to lateral. The osteotomy is also planned to increase the posterior tibial slope in the sagittal plane, which theoretically increases the anteroposterior component of the joint contact forces and reduces posterior subluxation of the tibia relative to the femur. Operative Procedure. All patients routinely receive a prophylactic dose of intravenous antibiotics preoperatively. General endotracheal anesthesia is preferred because of the potential need for an autogenous corticocancellous iliac crest graft. The patient is positioned supine, and the

6 Vol. 32, No. 1, 2004 Symptomatic Hyperextension-Varus Thrust 65 TABLE 3 Radiographic Outcome of All Patients a Preoperative Postoperative FT angle MA Slope BP FT angle MA Slope BP Grade OA (degrees) (percent) (degrees) ratio (degrees) (percent) (degrees) ratio (0 2) (5 to 9) (0 11) ( ) (0 11) (6 21) ( ) a OA = osteoarthritis; FT = femorotibial; MA = mechanical axis BP = Blackburne-Peel. involved limb and ipsilateral iliac crest are prepared and draped. Concurrent arthroscopy is performed as necessary to evaluate the menisci and the status of the articular cartilage. Following arthroscopy, the extremity is elevated, exsanguinated, and the rest of the procedure carried out under tourniquet control. A vertical incision is made over the pes anserinus insertion halfway between the medial border of the patella ligament and the posterior margin of the tibia. The sartorial fascia is incised exposing the hamstring tendons. Blunt retractors are placed anteriorly to protect the patellar ligament and posteriorly to protect the hamstring tendons and superficial medial collateral ligament. Under fluoroscopic control, a guide wire is drilled across the proximal tibia from medial to lateral. The guide is positioned at the level of the superior aspect of the tibial tubercle and oriented obliquely to end approximately 1 cm below the joint line at the lateral tibial cortex. The osteotomy is then performed with an oscillating saw below the guide pin to prevent superior migration and an intra-articular fracture. The osteotomy is deepened with flexible and rigid osteotomes using fluoroscopic confirmation. Once the osteotomy has been completed, the medial opening is created with an osteotomy wedge to the predetermined depth. Intraoperative femorotibial alignment is verified by fluoroscopy, and an alignment guide is used to ensure that the weightbearing axis is passing through the center of the knee joint. The posterior tibial slope is also assessed intraoperatively and can be changed by distracting the osteotomy more anteriorly or posteriorly. The slope is increased enough to correct the hyperextension deformity to neutral. If the opening is greater than 1 cm anteriorly, a tibial tubercle osteotomy is performed to advance the tubercle the same height of the osteotomy (Fig. 4). When the desired opening has been achieved, the osteotomy is secured with a plate and/or bone graft. Placement of fixation is confirmed with fluoroscopic imaging. Tourniquet is released and hemostasis controlled. The wound is closed in layers over a drain placed in the subcutaneous space. In our early experience with this technique, we used iliac crest bone grafting alone to secure the osteotomy in place (cases 1, 6, 10, and 15). Later, we secured the osteotomy with a two-hole or four-hole osteotomy plate (Arthrex, Naples, Florida). The plate is fixed proximally with 6.5- mm cancellous screws and distally with 4.5-mm cortical screws. Six patients (cases 2, 4, 7, 8, 9, and 12) did not have iliac crest bone grafting of the osteotomy site. We now recommend plate fixation and iliac crest bone grafting of all opening wedge osteotomies to prevent delayed or nonunion and fixation failure. Postoperative Regimen and Evaluation. Postoperatively, the osteotomy is protected in a hinged knee brace for 6 weeks. The patient is kept feather weightbearing with crutches for 6 weeks postoperatively. If there is radiographic evidence of union at 6 weeks, the patient is gradually advanced to partial weightbearing. Full weightbearing may commence at 12 weeks, with appropriate evidence of radiographic healing. Physiotherapy is used for range of motion exercises in the brace until the osteotomy has healed. Patients were followed postoperatively from the time of osteotomy to latest follow-up to determine the highest

7 66 Naudie et al. The American Journal of Sports Medicine A B C D Figure 4. (A) Preoperative anteroposterior radiograph of a 33- year-old male (case 14) with capsuloligamentous laxity and a severe hyperextension thrust. (B) Preoperative weightbearing lateral radiograph of the same patient. (C) Postoperative anteroposterior radiograph of the same patient after a 10-mm opening wedge osteotomy and tibial tubercle osteotomy fixed with a two-hole osteotomy plate (Arthrex, Naples, Florida) and iliac crest bone graft. (D) Postoperative weightbearing lateral radiograph of the same patient demonstrating an increase in posterior tibial slope and improvement in the hyperextension deformity.

8 Vol. 32, No. 1, 2004 Symptomatic Hyperextension-Varus Thrust 67 level of activity that had been achieved after osteotomy. Patients were also asked to complete a 5-point visual analogue scale to assess the stability of their knee compared to before the osteotomy. Patients were advised to assess each leg independently if both sides had been treated. The level of change was rated as significantly better, somewhat better, same, somewhat worse, or significantly worse. Patients were also asked to assess whether they were satisfied with the operation and if they would have the operation again given the same circumstances. Postoperative femorotibial axis alignment, mechanical axis alignment, posterior tibial slope, and the ratio of patellar height were measured on full-length standing anteroposterior and lateral radiographs at 1 year after osteotomy. The degree of correction of femorotibial and mechanical axis alignment and the change in posterior tibial slope and patellar height were calculated for all patients. Any complications or further surgeries were evaluated. RESULTS Outcomes for all patients are displayed in Tables 2 and 3. The 16 patients were followed for an average of 56 months (range, 35 to 110 months) after the osteotomy. The average functional activity score of Tegner and Lysholm was 3.25 points (range, 0 to 6 points) preoperatively. Two patients (cases 4 and 13) were on permanent disability secondary to their knee symptoms prior to osteotomy. The average functional activity score of Tegner and Lysholm was 5.25 points (range, 1 to 9 points) postoperatively. All patients had an increase in their score postoperatively. Of the 2 patients on disability, one patient (case 4) was able to return to sedentary work; the other patient (case 13) was able to return to work driving a transport truck. The greatest increase in score was observed in a young hockey player (case 5) who sustained a combined PCL and posterolateral ligament injury on an all-terrain vehicle and returned to play hockey at the semiprofessional level following osteotomy alone. All patients felt that knee stability had improved with osteotomy. All but 1 patient (case 13) was satisfied with the surgery and would have it again given the same circumstances. This patient was dissatisfied because he fell after his initial surgery and displaced his tibial tubercle osteotomy, which required reoperation. Full-length standing anteroposterior and lateral radiographs taken at 1 year postoperatively were available for review for all patients. No patients demonstrated significant osteoarthritic changes according to the radiographic grading system of Koshino and Machida. 15 The average preoperative femorotibial alignment was 0 (range, 9 varus to 5 valgus), and the average postoperative femorotibial alignment was 6 valgus (range, 0 to 11 ). The average change in alignment was 6 of valgus. The average preoperative mechanical axis alignment was 18% toward the lateral compartment, and the average postoperative mechanical axis alignment was 46% toward the lateral compartment. The average change in the mechanical axis alignment was 28% from medial to lateral. The average preoperative tibial slope measured 6 of posterior inclination (range, 0 to 11 ), and the average postoperative tibial slope measured 14 of posterior inclination (range, 6 to 21 ). The average change in tibial slope was 8 of posterior inclination. The average preoperative ratio of patellar height was 0.89 (range, 0.63 to 1.14), and the average postoperative ratio of patellar height was 0.72 (range, 0.53 to 1.00). All patellas were lowered with the osteotomy, and the average decrease in the ratio of patellar height was According to the Blackburne and Peel method, 3 patella infera is present when the ratio of patellar height is less than 0.54, and two patients (cases 4 and 11) developed patella infera in this series. Eight patients required reoperation following osteotomy. One patient (case 13) displaced his tibial tubercle osteotomy with a fall postoperatively and required revision of the displaced osteotomy. Two patients (cases 15 and 17) required removal of symptomatic hardware only. Five patients (cases 1, 6, 8, and 11) went on to delayed PCL reconstruction, one of whom also underwent delayed posterolateral ligament advancement and removal of hardware. All five patients had hoped to gain further improvements in knee stability with PCL reconstruction. DISCUSSION Many studies have shown that HTO for unicompartmental osteoarthritis and varus malalignment of the knee produces satisfactory clinical results. 6,13,14,22,23 Very few studies, however, have looked at the functional outcome of HTO alone for instability and malalignment. 2,11,12 We have used an opening wedge osteotomy to treat several young, active patients with a symptomatic hyperextension-varus thrust in the absence of significant osteoarthritis. The purpose of this study was to describe and assess the functional and radiographic results of our operative technique. The contribution of sagittal plane deformity to knee stability in ligament deficient knees has recently received considerable attention. In a biomechanical study, Bonnin 4 found the load on the ACL to be greater when the posterior slope of the tibia exceeded a threshold value of 10 posterior inclination during weightbearing. In a radiographic analysis of 281 cases, Dejour and Bonnin 7 noted a linear correlation between the tibial slope and tibial translation during monopedal weightbearing. Together, these authors theorized that decreasing posterior tibial slope in the sagittal plane decreases the anteroposterior component of the joint contact forces and reduces anterior subluxation of the tibia relative to the femur, thus improving symptoms of anterior instability. Conversely, they theorized that increasing posterior tibial slope increases the anteroposterior component of the joint contact forces and reduces posterior subluxation of the tibia relative to the femur, thus improving symptoms of posterior instability. Several follow-up studies suggest that lateral closing wedge osteotomies tend to decrease posterior tibial slope, whereas medial opening wedge osteotomies tend to increase tibial slope. 1,18 In fact, several authors have sug-

9 68 Naudie et al. The American Journal of Sports Medicine A B C Figure 5. (A) In the normal knee with intact PCL and posterolateral ligaments, the weightbearing line passes through the center of the knee joint during gait. (B) In the PCL or posterolateral ligament-deficient knee, the lateral soft tissues separate and the weightbearing line passes through the medial compartment, resulting in a varus thrust during gait. (C) A properly performed medial or anteromedial opening wedge osteotomy results in a weightbearing line that passes through the center of the knee (a point 50% of the width of the tibial plateau) and improvement of the varus thrust during gait but no change in the static ligamentous laxity. gested using lateral closing wedge high HTOs for patients with chronic ACL-deficient knees. 8,9,18,25,27 Our group has previously reported good functional results in a small group of patients using the lateral closing wedge osteotomy alone in the treatment of chronic ACL deficiency. 11 HTO combined with ACL reconstruction has also been shown to produce good clinical results in younger patients with varus malalignment and ACL deficiency. 9,16,18,24,25,27 For the same theoretical reasons outlined above, opening wedge osteotomies have been used with some success to treat hyperextension and recurvatum deformities of the knee. Lecuire et al. 17 reported good results in 44 opening wedge HTOs combined with tibial tubercle elevation for hyperextension deformities of the knee. Similarly, Moroni et al. 21 reported good results with anterior opening wedge osteotomy in 25 patients with genu recurvatum. These

10 Vol. 32, No. 1, 2004 Symptomatic Hyperextension-Varus Thrust 69 authors, however, treated predominantly osseous deformities and found that they had poor results when the deformity was primarily in the ligaments, capsule, or soft tissues. The patients in our series represented a unique group of young, active individuals with severely affected knees, most of whom had undergone previous operative procedures. All patients in our series had ligamentous or capsuloligamentous laxity with varus knee alignment and presented with a functionally disabling hyperextension-varus thrust. These patients present a difficult problem to the orthopaedic surgeon because soft-tissue procedures alone are often unsatisfactory as the uncorrected alignment leads to repetitive stresses and failure of the surgically reconstructed structures. Noyes and Barber-Westin 26 agree that surgical restoration of chronic deficiency of the posterolateral complex should not be performed in varusaligned knees until the alignment has been corrected. Wirth and Peters 31 have reviewed their experience with multiply reoperated knee instabilities and suggest that the specific problem of the patient should be addressed and solved with the most limited procedure possible. We agree with these authors, and our approach to patients who present with a symptomatic hyperextension-thrust has been to first address the coronal and sagittal plane alignment with osteotomy, then deal with residual ligamentous laxity. The objective of the osteotomy is to eliminate the hyperextension-varus thrust during gait, realizing that it does not eliminate static ligamentous laxity (Fig. 5). In our opinion, the opening wedge technique allows easier correction of coronal and sagittal plane deformities than traditional osteotomy techniques. Moreover, this technique allows preservation of bone stock and normal proximal tibial anatomy without disruption of the proximal tibiofibular joint. This is especially important in knees that have already had surgery to the lateral side or that may require further surgery on the lateral side to correct residual instability. This technique also avoids the peroneal nerve and does not violate the muscles of the anterior compartment, thereby decreasing the likelihood of peroneal nerve palsy or compartment syndrome. Finally, this technique theoretically tightens the capsuloligamentous structures around the knee, which is advantageous in the ligament-deficient knee. One disadvantage of this technique is that it does require autologous or allograft bone grafting, and bony consolidation may take longer in comparison to a lateral closing wedge technique. In this series of 16 patients, the average Tegner and Lysholm activity score increased by two points following osteotomy. All patients had an increase in their activity score postoperatively. All patients felt that knee stability had improved with osteotomy. All but 1 patient was satisfied with the surgery and would have it again given the same circumstances. Using the same functional activity score, Nagel et al. 22 looked at patients treated with HTO for medial compartment osteoarthritis and varus alignment of the knee. In contrast to the current study, these authors found that level of activity was not improved with osteotomy but at best maintained at the preoperative level. Although patients had a high average patient-satisfaction score in their study, 6 of the 34 patients stated they would not have the operation again given the same circumstances. In this series, the average correction of alignment in the coronal plane was 6 of femorotibial valgus. The optimal correction recommended for varus knee deformities in osteoarthritis varies according to author. Coventry et al. 6 suggested overcorrecting the varus alignment to 8 or more of femorotibial valgus based on a regression analysis of the longevity of lateral closing wedge osteotomies. Other authors have reported optimal results when a 3 to 6 valgus mechanical axis had been achieved. 13,19 We plan the osteotomy to move the weightbearing line through a point 50% of the width of the tibial plateau. In our experience, it is important that the knee is not overcorrected, as is the case of the osteoarthritic knee. We were successful in correcting the mechanical axis to an average of 46% toward the lateral compartment in this study. This represented a change of 28% along the width of the tibial plateau. The tibial slope was increased a mean of 7 of posterior inclination. Very few recommendations have been made regarding optimal correction of sagittal alignment and posterior tibial slope. We do know that sagittal plane deformity must be carefully considered in cruciate ligament deficient knees. 5,8 We assess the posterior tibial slope intraoperatively and change it by distracting the osteotomy more anteriorly or posteriorly. Our aim is to increase the posterior tibial slope enough to correct any hyperextension deformity to neutral. In this study, the ratio of patellar height was decreased an average of Two patients developed patella infera following surgery. Using the same method as the current study, Scuderi et al. 28 evaluated patellar height in 66 knees following lateral closing wedge osteotomy. These authors reported a lower average decrease of 0.10 in the ratio of patellar height with the lateral closing wedge technique. They also reported that 76% of patellae were lowered with this technique and that patella infera was present in 5 of the knees following surgery. They found no correlation between postoperative height of the patella, however, and the need for subsequent revision to a total knee arthroplasty. Similarly, we found no correlation between postoperative patellar height and functional outcome, although the numbers in our series were too small for statistical analysis. The decrease in patellar height observed remains a theoretical concern with this technique because of its effect on patellofemoral contact forces. There were no cases of intra-articular fracture, nonunion, peroneal nerve palsy, compartment syndrome, or avascular necrosis in this series. One patient (case 3) showed evidence of delayed union at 3-month follow-up but was treated with prolonged protected weightbearing and went on to unite the osteotomy uneventfully. One patient did require revision of the tibial tubercle osteotomy because of traumatic displacement. Our only recommendation for prevention of these complications is to protect the osteotomy until there is evidence of radiographic

11 70 Naudie et al. The American Journal of Sports Medicine union. Three patients required removal of symptomatic hardware, which we have not previously found to be a problem with this technique. Five patients went on to delayed PCL reconstruction, but all had demonstrated some improvement in functional activity level with osteotomy alone. These 5 patients hoped to gain further improvement in stability and function with PCL reconstruction. We feel that had these patients been treated with ligament reconstruction alone (without correction of malalignment), the soft-tissue reconstruction would have likely stretched out and eventually failed. Therefore, we felt that osteotomy was successful in avoiding further ligament reconstructive surgery in 11 of the 16 patients, or nearly 70% of the patients. We fully recognize several limitations of this study. Foremost, we realize that this study was retrospective and therefore subject to the problems and biases inherent to this type of study design. Second, we recognize that the indications for osteotomy in this study were not based on fixed clinical or radiographic criteria. Third, we acknowledge that clinical evaluation of change in knee stability could have been better assessed using arthrometric testing. Unfortunately, such assessment was not possible, as no preoperative measurements had been recorded for comparison. Nonetheless, the early results of this clinical study suggest that opening wedge HTO can produce good functional and radiographic results in selected patients. We believe that mechanical axis realignment and sagittal plane correction are fundamental considerations in the management of complex knee instability presenting as a symptomatic thrust. 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