Serial Changes in the Joint Space Width and Joint Line Convergence Angle After Closed-Wedge High Tibial Osteotomy

Abstract

Background:

There have been little data concerning serial changes in the joint space width (JSW) and joint line convergence angle over the course of follow-up periods after closed-wedge high tibial osteotomy (CWHTO).

Purpose:

To evaluate serial changes in the JSW and joint line convergence angle after CWHTO.

Study Design:

Case series; Level of evidence, 4.

Methods:

A total of 100 computer-assisted CWHTOs with a minimum follow-up period of 3 years (mean, 4.4 years) were analyzed. Clinically, the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score was evaluated. Radiographically, the mechanical axis was measured preoperatively and postoperatively. The minimal JSW was measured as the shortest distance between the femur and the tibia. The convergence angle was measured as the angle between the tangent to the subchondral plates of the femoral condyle and the tibial plateau. Serial changes in these measurements were analyzed preoperatively; at 3 months, 6 months, 1 year, and 2 years postoperatively; and at the final follow-up. The intraclass correlation coefficients for all measurements were greater than 0.8.

Results:

The mean WOMAC score improved from 41.4 preoperatively to 14.9 at the final follow-up. The preoperative and postoperative mean mechanical axis was 8.1° varus and 1.6° valgus, respectively. The mean minimal JSW was 2.5, 2.9, 2.9, 3.1, 3.2, and 3.1 mm preoperatively and at 3 months, 6 months, 1 year, 2 years, and the final follow-up, respectively (P < .001). The mean convergence angle was 4.4°, 3.9°, 4.0°, 4.1°, 4.2°, and 4.3°, respectively, during the same time periods (P = .068).

Conclusion:

Cartilage healing, as indicated by the JSW, and clinical improvement were maintained over the minimum 3-year follow-up after CWHTO. Cartilage pressure, as indicated by the convergence angle, remained unchanged after CWHTO.

Keywords

knee osteoarthritis osteotomy closed wedge joint space width convergence angle

High tibial osteotomy (HTO) is an effective surgical treatment option for unicompartmental osteoarthritis of the knee with a varus deformity. Two basic techniques are available, medial open-wedge HTO and lateral closed-wedge HTO (CWHTO), each of which has particular advantages and disadvantages. Surgeons at our institution have tended to prefer CWHTO because of the benefits of rapid bone healing and possible early rehabilitation in relatively old patients.^5-7 Realignment of the weightbearing axis by HTO can alter the forces acting on articular cartilage within the knee, reducing the load on the medial compartment.^2,22,26 The procedure is thought to allow repair of the articular surface or arrest further cartilage degeneration.^13,17,32 In contrast to the frequent application of HTO in clinical practice, the biomechanical evidence regarding cartilage quality remains largely unclear. The repaired cartilage is thought to be predominantly fibrous cartilage. The degree of cartilage restoration and whether it can endure the weightbearing load over midterm to long-term follow-up periods are still to be determined.

Previous studies evaluated repaired cartilage after HTO using various methods such as the delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) method^8,26,29 and second-look arthroscopic surgery or histology.^19,34 The dGEMRIC method is useful for measuring the glycosaminoglycan concentration in repaired cartilage,^8,29 but it is unable to measure the concentration quantitatively in patients with retained metal fixation devices after HTO or during weightbearing. Previous in vivo studies described the effect of realignment on cartilage repair using second-look arthroscopic surgery and histology.^18,19,34 However, the performance of routine arthroscopic surgery and a histological biopsy is not useful for determining cartilage quality after HTO because the small fixation devices do not need to be removed in most patients after CWHTO and there are few chances to perform second-look arthroscopic surgery.

The joint space width (JSW) on radiographs also has been evaluated as a surrogate measure for cartilage thickness.^18,37 It is considered to be the simplest and easiest method to evaluate cartilage of the knee joint. A small number of studies have measured the JSW radiographically after HTO.^18,37 It was reported that patients with a greater degree of cartilage repair after open-wedge HTO or knee joint distraction more frequently showed an increased JSW than patients with little to no repair.³⁷ Another study reported that patients with increased cartilage repair after CWHTO showed an increased JSW.¹⁸ If the minimal JSW is increased, we wanted to investigate when it is largely increased and how long the JSW endures after HTO. However, there have been very little data concerning the serial change in, and the size of, the JSW over the course of a midterm to long-term follow-up period.

One of the goals after HTO is to decrease cartilage pressure in the medial compartment of the femorotibial joint. A medial metaphyseal opening in open-wedge HTO can increase medial soft tissue tension and cartilage pressure, despite the fact that the mechanical axis (MA) has been shifted toward valgus.² Several previous clinical studies reported a considerable change in the joint line convergence angle after open-wedge HTO.^25,31 In contrast, it is considered that CWHTO might not influence the convergence angle and cartilage pressure secondary to changes in soft tissue tension of the medial collateral ligament (MCL).^7,11,24 The procedure may instead decrease it secondary to functional laxity away from the center of rotation.^7,11,24 To our knowledge, no previous data exist regarding the change in the convergence angle after CWHTO. In addition, it remains unclear whether the extent of the correction angle in the coronal plane significantly affects the convergence angle after CWHTO.

The purpose of the present study was to evaluate serial changes in the JSW and joint line convergence angle after CWHTO. It was hypothesized that the JSW would be increased after CWHTO and would remain so during the midterm follow-up period. It was also hypothesized that the convergence angle would be unchanged and would be unaffected by the degree of correction angle after CWHTO.

Methods

Consecutive data were prospectively obtained from patients who underwent computer-assisted CWHTO between December 2008 and February 2012. The VectorVision computed tomography–free navigation system (version 1.1; BrainLAB) was used, and a Miniplate staple (U&I) was used as a fixative. The inclusion criterion for the study was medial compartment osteoarthritis (Kellgren-Lawrence grades 2-4⁹) associated with a varus deformity >10°. The exclusion criteria for HTO were (1) flexion contracture >15°, (2) a flexion angle <90°, (3) lateral compartment osteoarthritis (Kellgren-Lawrence grades 3-4), (4) lateral tibial subluxation >10 mm, (5) expected postoperative joint line obliquity after HTO >5°, and (6) diseases other than primary osteoarthritis such as inflammatory arthritis or traumatic arthritis after ligament injuries. A total of 100 computer-assisted CWHTOs (94 patients) were enrolled in this study. The mean follow-up period was 4.4 ± 2.9 years (range, 3.0-9.7 years). The demographics of both groups are shown in Table 1.

Table 1

Preoperative Demographics and Clinical Status

	Value
No. of cases	100
No. of patients	94
Age, y, mean ± SD (range)	58.7 ± 7.4 (41-72)
Sex, female/male, n	89/5
Body mass index, kg/m², mean ± SD (range),	25.0 ± 2.7 (17.3-31.4)
Side, right/left, n	58/42
Kellgren-Lawrence grade, 1/2/3/4, n	0/37/59/4
Follow-up period, y, mean ± SD (range)	4.4 ± 2.9 (3.0-9.7)

We estimated the sample size required to detect differences in the JSW and joint line convergence angle among preoperative and serial postoperative values using repeated-measures analysis of variance. We determined that a minimum of 43 knees were required to detect these differences, with a type I error of 0.05 and a power of 0.8. With 100 knees, the power of the present study was 99%. This result verified the adequacy of the sample size in this study. The study was approved by the institutional review board of our hospital (KHUH201702002-HE002).

Surgical Technique and Rehabilitation

Computer-assisted CWHTO was performed as described previously.^6,7 The tibialis anterior muscle was dissected subperiosteally from the tibia and reflected distally. Partial resection of the fibular head was performed with an osteotome and a pituitary rongeur to prevent a tethering effect of the fibula during the wedge closing. The standard registration procedure for computer-assisted CWHTO was applied depending on the requirements of the system used. The postoperative MA percentage (MA%) was targeted to be 62%. The navigation system set the cut plane of the osteotomy site perpendicular to the MA according to the sagittal plane. An additional slope was fine tuned in the planned osteotomy site, in keeping with the posterior slope angle (PSA) measured on the preoperative radiograph. A precalibrated navigation drill guide was used to place 2 K-wires in the proximal plane of the osteotomy site and another 2 K-wires in the distal plane. Posterior displacement of the proximal fibula after partial resection of the fibula head could help in attaining an accurate location of the hinge axis to be perpendicular to the coronal plane with careful configuration of the proximal tibia and K-wire direction. In addition, the anterior and posterior heights of the wedge were rendered symmetrical using this 4-pin guide technique to avoid unwanted changes in the tibial PSA.⁴ Proximal and distal osteotomies were carried out using a sharp electric saw over 2 K-wires. The wedge was removed and the osteotomy site carefully closed. Next, the osteotomy site was rigidly fixed using a Miniplate staple. A systematic rehabilitation protocol was used: straight-leg raising exercises were started 3 days postoperatively, partial weightbearing was begun 1 week postoperatively, and full weightbearing without crutches was started at 6 to 12 weeks based on the patient’s condition.

Clinical Evaluation

The clinical results were evaluated in terms of the Knee Society knee and function scores, the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, and range of motion. Any complications that occurred were recorded.

Radiographic Evaluation

Radiographically, the MA and MA% were measured from full-length, weightbearing anteroposterior radiographs of the leg, including the hip, knee, and ankle (an orthoroentgenogram).^6,7 The PSA of the tibia was measured from a true lateral view of the knee. The minimal JSW and joint line convergence angle were measured from true anteroposterior radiographs of the knee. The radiographs were taken the day before and 2 weeks after surgery and were also taken at 3 months, 6 months, 1 year, 2 years, and the final follow-up. The quality of radiographic evaluations was improved by the radiographic protocol of standardization in the position of the knee and an identical distance between the X-ray beam and cassette.⁵ The distance between the radiographic source and the patient’s bone was 245 cm, and that between the radiographic source and the cassette was 260 cm. The images were transferred digitally to a picture archiving and communication system (PACS) and were then manipulated. Assessments were performed on a 61-cm (24-inch) monitor (SyncMaster 2494HM; Samsung) in portrait mode using PACS software (Infinite). The minimum differences that the software could detect were 0.1° in angle and 0.1 mm in length.

The MA for coronal plane alignment was defined as the angle between the femoral and tibial mechanical axes. The MA% was defined as the percentage by which the MA bisected the total width of the tibia. The correction angle was defined as the difference between the preoperative and postoperative MA. The tibial intramedullary reference line of the PSA was defined as the line connecting the center of the medullary canal 10 and 20 cm distal to the tibial plateau. The PSA itself was defined as the angle formed by a line perpendicular to the reference line and the medial tibial plateau.⁴ The change in the PSA was considered to be the difference between the preoperative and postoperative PSA, with a positive value indicating an increase in the PSA.

The minimal JSW was measured as the shortest distance between the medial femoral condyle and the medial tibial plateau (Figure 1A).^13,18,37 The radiographic magnification of the minimal JSW measurements was corrected using standardization and the PACS ruler. The minimal JSW was recorded in millimeters, rounded to one decimal place. The convergence angle was measured as the angle between the tangent to the subchondral plates of the femoral condyle and the tibial plateau (Figure 1B).^20,31,35 A positive value indicates the medial convergence of 2 lines that were drawn by the subchondral plate of the femoral condyle and the tibial plateau. They were evaluated serially to determine changes in the minimal JSW and convergence angle.

To reduce observation bias, 2 independent investigators (C.H.P. and J.W.L.) carried out all of the radiographic measurements. The investigators were orthopaedic surgeons who did not participate in the surgical procedure and had more than 5 years of clinical experience. The intraobserver and interobserver reliabilities of the measurements were assessed using the intraclass correlation coefficient. In this study, the intraclass correlation coefficients for all measurements were greater than 0.80 (range, 0.81-0.97) for the intraobserver and interobserver reliabilities. Thus, measurements taken by one investigator (C.H.P.) were used in the analyses.

Statistical Analysis

The preoperative and postoperative clinical and radiographic results were compared using a paired t test. The serial data for the minimal JSW and convergence angle were compared (repeated-measures analysis of variance). The change in the minimal JSW was analyzed according to the correction angle (using Pearson correlation analysis) to evaluate whether the degree of MA correction affected cartilage repair. The change in the convergence angle was analyzed according to the correction angle (using Pearson correlation analysis) to evaluate whether a large wedge size decreased the convergence angle. The clinical results were compared between groups in which the minimal JSW had increased or decreased and also between the increased and decreased convergence angle groups.

Statistical analyses were performed using SPSS version 20.0 (SPSS), and P values <.05 were considered to be statistically significant.

Results

Clinical Results

The mean Knee Society knee score increased from 74.2 ± 5.1 before surgery to 87.1 ± 5.1 at the final follow-up (P < .001), while the mean function score increased from 73.7 ± 7.1 to 85.9 ± 6.4 (P < .001). The mean WOMAC score improved from 41.4 ± 12.8 before surgery to 14.9 ± 3.8 at the final follow-up (P < .001). The mean preoperative flexion contracture was 1.4° ± 3.3°, and the mean postoperative flexion contracture was 0.4° ± 1.7° (P = .004). The mean preoperative maximum flexion angle was 137.7° ± 10.1°, and the mean postoperative maximum flexion angle was 139.0° ± 6.1° (P = .201). No complications such as infections, neurovascular injuries, and delayed union or nonunion occurred.

Radiographic Results

The mean MA was 8.1° ± 2.9° varus (range, 15.0° varus to 3.2° varus) preoperatively and 1.6° ± 1.9° valgus (range, –0.9° varus to 7.7° valgus) postoperatively (P < .001). The proportion of ±3° outliers in the postoperative MA was 5 knees when the postoperative MA target was set to be 2° to 3° valgus. The mean correction angle was 9.7° ± 3.0°. The mean preoperative and postoperative MA% were 12.7% ± 13.8% and 57.5% ± 7.9%, respectively (P < .001). The mean preoperative PSA was 10.1° ± 3.1°, and the mean postoperative PSA was 9.3° ± 2.7° (P = .203).

The mean minimal JSW was 2.5 ± 1.3, 2.9 ± 1.4, 2.9 ± 1.3, 3.1 ± 1.4, 3.2 ± 1.3, and 3.1 ± 1.5 mm preoperatively; at 3 months, 6 months, 1 year, and 2 years postoperatively; and at the final follow-up, respectively (Figures 2 and 3). There was a significant increase in the minimal JSW at 3 months, and it was then maintained up to 3 years (P < .001). No joint space narrowing or increase was observed in 73% of knees (57% of all knees had a minimal JSW of >0.5 mm) after a minimum of 3 years and a mean 4.4 years of follow-up (Table 2).

Table 2

Distribution of Cases According to the Change in the Minimal Joint Space Width

Change, mm	No. of Knees	Cumulative Percentage
<–2.0	6	6
−2.0 to −1.5	3	9
−1.5 to −1.0	3	12
−1.0 to −0.5	4	16
−0.5 to 0	11	27
0 to 0.5	16	43
0.5 to 1.0	16	59
1.0 to 1.5	18	77
1.5 to 2.0	11	88
>2.0	12	100

The mean convergence angle was 4.4°, 3.9°, 4.0°, 4.1°, 4.2°, and 4.3°, respectively, over the same time periods (Figure 2). There was no significant difference in the serial data for the convergence angle (P = .068). The change in the minimal JSW was not correlated to the postoperative MA (P = .214). The change in the minimal JSW was, however, positively correlated to the correction angle (r = 0.327, P = .001), and there was a negative correlation between the correction angle and the change in the convergence angle (r = −0.362, P < .001). The larger the correction angle, the more decreased the postoperative convergence angle was or the less it tended to converge medially.

Comparison of Clinical Results According to Minimal JSW or Convergence Angle

No difference was identified in the knee and function scores, WOMAC scores, and range of motion between the increased and decreased minimal JSW groups (P = .618, .121, .661, and .479, respectively) (Table 3). There was also no difference in clinical results between the increased and decreased convergence angle groups (P = .294, .103, .433, and .119, respectively) (Table 4).

Table 3

Comparison of Clinical Outcomes Between the Increased Minimal JSW Group and Decreased Minimal JSW Group^a

	Increased or No Change^b (n = 75)	Decreased^c (n = 25)	P Value
Knee score
Preoperative	74.3 ± 5.1	74.0 ± 5.1	.750
Last follow-up	87.3 ± 4.7	86.6 ± 6.3	.618
Function score
Preoperative	73.5 ± 7.7	74.2 ± 5.1	.668
Last follow-up	85.0 ± 6.0	87.4 ± 7.2	.121
WOMAC score
Preoperative	41.7 ± 13.2	40.5 ± 12.0	.675
Last follow-up	15.1 ± 3.8	14.3 ± 3.8	.661
Range of motion, deg
Preoperative	137.1 ± 11.1	139.4 ± 6.2	.333
Last follow-up	139.2 ± 6.0	138.2 ± 6.4	.479

Values are presented as mean ± SD. JSW, joint space width; WOMAC, Western Ontario and McMaster Universities Osteoarthritis Index.

Cases in which the minimal JSW at last follow-up was greater than or equal to the preoperative minimal JSW.

Cases in which the minimal JSW at last follow-up was less than the preoperative minimal JSW.

Table 4

Comparison of Clinical Outcomes Between the Increased JLCA Group and Decreased JLCA Group^a

	Increased or No Change^b (n = 50)	Decreased^c (n = 50)	P Value
Knee score
Preoperative	74.0 ± 5.0	74.5 ± 5.1	.609
Last follow-up	87.6 ± 5.2	86.5 ± 5.0	.294
Function score
Preoperative	72.7 ± 8.5	74.6 ± 5.3	.192
Last follow-up	86.9 ± 6.8	84.8 ± 6.0	.103
WOMAC score
Preoperative	43.2 ± 14.1	39.6 ± 11.2	.162
Last follow-up	14.6 ± 3.7	15.2 ± 3.9	.433
Range of motion, deg
Preoperative	138.0 ± 10.3	137.4 ± 10.0	.768
Last follow-up	138.0 ± 7.1	139.9 ± 4.7	.119

Values are presented as mean ± SD. A positive value indicates medial convergence of 2 lines that were drawn by the subchondral plate of the femoral condyle and the tibial plateau. JLCA, joint line convergence angle; WOMAC, Western Ontario and McMaster Universities Osteoarthritis Index.

Cases in which the JLCA at last follow-up was greater than or equal to the preoperative JLCA.

Cases in which the JLCA at last follow-up was less than the preoperative JLCA.

Discussion

The most important finding of the present study was that the minimal JSW was increased at 3 months postoperatively and then stabilized along with clinical improvement for at least 3 years after CWHTO (Figure 3). There were 73 knees with an increased minimal JSW at the last follow-up. The minimal JSWs of 2 knees remained unchanged, and those of 25 knees decreased during the follow-up period. The unloading of articular cartilage in the medial compartment is considered to be a therapeutic goal to slow or prevent the progression of osteoarthritis or even cartilage repair.²² The JSW has been evaluated as a surrogate measure for cartilage thickness.³⁷ van der Woude et al³⁷ reported that the amount the minimal JSW increased by was 0.4 ± 0.5 mm at 1 year after open-wedge HTO and 0.8 ± 1.0 mm after a knee joint distraction procedure. Our increase was 0.6 ± 1.5 mm at 1 year after CWHTO, and it remained at this level during a minimum of 3 years and a mean 4.4 years of follow-up. Previous studies showed similar widening of the medial joint space, ranging from 0.4 mm to 1.1 mm, but did not report the serial change in the minimal JSW or the endurance of healed cartilage.^30,37 Huizinga et al¹³ reported that the minimal JSW changed from 3.4 ± 1.5 mm preoperatively to 3.3 ± 1.6 mm at an average follow-up of 5.2 years. No joint space narrowing or increase in space was observed in 52% of patients, and 31% of all patients increased their minimal JSW by more than 0.5 mm. In the present study, no joint space narrowing or increase in space was observed in 73% of knees, and 57% of all knees increased their minimal JSW by more than 0.5 mm. The difference with respect to our data was the small proportion of patients with a decreasing minimal JSW after HTO (27% in the current study’s knees vs 48%¹³) (Table 2).

The increased JSW can be explained either by the formation of repaired cartilage or by the mechanical effect of transferring the weightbearing alignment of the limb to the lateral compartment, or a combination of both.^13,14,19 Koshino et al¹⁸ reported that patients with increased cartilage repair after CWHTO showed an increased minimal JSW more frequently than patients with little to no repair. Progressive narrowing of the JSW in osteoarthritic knees has been studied without treatment.^10,27 The fact that there was no progressive narrowing of the minimal JSW in 73% of knees after the midterm follow-up period according to our data could provide evidence of the advantage of HTO in delaying or even preventing the progression of osteoarthritis and further surgery.

A significant correlation is known to exist between the preoperative convergence angle and the severity of osteoarthritis as evaluated by the Ahlbäck grade.³⁸ The radiographic severity of osteoarthritis is most frequently classified by the Kellgren-Lawrence and Ahlbäck grades.²⁸ It is known that the agreement between Kellgren-Lawrence grades 2 to 3 versus Ahlbäck grade 1 as well as Kellgren-Lawrence grades 3 to 4 versus Ahlbäck grades 1 to 2 is good.²⁸ The correlation between the preoperative convergence angle and the severity of osteoarthritis can be expected whatever classification system is used. The convergence angle can represent soft tissue contracture or laxity around the knee joint.^20,25,31 This soft tissue tension can affect intra-articular pressure in the knee joint.^1,12 A medial open-wedge procedure increases the strain of the superficial MCL because spreading of the osteotomy gap is carried out intraligamentously between the 2 insertion points of the MCL. Such overtensioning of the MCL and increased cartilage pressure are inevitable after open-wedge HTO without MCL release.² It can be assumed that the medial compartment of the knee joint has been adequately decompressed by releasing the distal fibers of the MCL in open-wedge HTO.² Decompression of the medial compartment in the knee joint after HTO can improve the flow of synovial fluid feeding the articular cartilage and may provide a beneficial effect on the metabolism of cartilage.²² In addition, too great a change in the convergence angle may lead to the risk of overcorrection in open-wedge HTO.²⁰

However, in all likelihood, CWHTO only has a minor effect on the MCL. Indeed, it may lead to a decrease in the convergence angle or allow it to become more parallel secondary to functional laxity of the MCL away from the center of rotation.^7,11,24 As predicted, there was no large serial change in the convergence angle in our study, in comparison to open-wedge HTO. It was reported that the change in the convergence angle ranged from −1.2° to −2.3° in open-wedge HTO,^20,25 while the serial change in the convergence angle in the present study ranged from −0.1° to −0.5° in CWHTO. We consider that the preservation of the convergence angle and avoidance of an increase in intra-articular pressure are among the advantages of CWHTO.

The fact that there was no correlation between the postoperative MA and a change in the minimal JSW was contrary to our expectations. Kanamiya et al¹⁴ suggested that overcorrection by as much as an MA% of 75% correlated with both a visible improvement in the articular surface and the functional score in CWHTO. Kumagai et al¹⁹ also showed that postoperative valgus alignment of the limb affects cartilage repair in second-look arthroscopic surgery, with an odds ratio of 1.18 (P = .01). However, Tsukada and Wakui³⁶ reported that no significant differences were found in the ratio of cartilage repair between overcorrected and moderately corrected knees. In the present study, the change in the minimal JSW and postoperative widening of the joint space were not correlated to the postoperative MA but rather to the correction angle. The postoperative MA ranged from –0.9° varus to 7.7° valgus in the present study, and the proportion of outliers of ±3° was only 5% when the postoperative MA target was set to be 2° to 3° valgus. We thought that the lack of correlation between the postoperative MA and minimal JSW might be caused by the narrow range of postoperative MA and small proportion of outliers, and this finding coincided with the results of Tsukada and Wakui.³⁶

Interestingly, there was a weak negative correlation between the change in the convergence angle and the correction angle. In other words, the larger the correction angle, the more decreased the postoperative convergence angle was or the less it tended to converge medially. The effect of the correction angle on the convergence angle might indirectly be to increase the change in the minimal JSW. However, further biomechanical studies in consideration of the intra-articular pressure will be needed to determine whether decreasing the intra-articular pressure with a decreasing convergence angle might stimulate cartilage repair and increase the postoperative minimal JSW.

Several studies have reported low correlations between clinical outcomes and radiographic,^18,33,37 second-look arthroscopic,^19,21,39 histological,^3,15 or magnetic resonance imaging²⁹ parameters of cartilage healing. The reason for these low correlations in the previous studies is unclear. van der Woude et al³⁷ reported that cartilage repair and the radiographic JSW were slightly better for a knee joint distraction procedure, whereas the clinical scores were slightly better for HTO.

The quality of repaired cartilage is clinically more important than the cartilage volume and the radiographic severity of osteoarthritis,⁴⁰ and we considered that the functional cartilage thickness could be evaluated on weightbearing radiographs. However, our results showed that there was still no correlation between the change in the minimal JSW and the clinical outcomes. It is possible that the accuracy in the degree of postoperative realignment or other confounding factors such as the activity level or body mass index (BMI) outweighs the subtle change in the minimal JSW and the amount of repaired fibrocartilage. The mean postoperative MA was 1.6° ± 1.9° valgus (range, –0.9° varus to 7.7° valgus) in the present study, and the proportion of outliers of ±3° was 5% by using the navigation system with improving surgical accuracy. We thought that there could be no correlation between the minimal JSW and the clinical results in patients with above range of postoperative MA in the midterm follow-up evaluation. Further studies of clinical scoring systems and various affecting factors, in consideration of the ceiling effect, will be needed to determine the prognostic factors of cartilage healing in addition to the radiographic, second-look arthroscopic, histological, or magnetic resonance imaging parameters.

The present study has several limitations. First, our patients comprised a prospective cohort in whom most of the data were collected prospectively; however, the convergence angle was instead measured retrospectively. The mean follow-up of 4.4 years was not long enough to evaluate the long-term endurance of cartilage healing after HTO. An optimal study would include a large, prospective randomized controlled trial with a control group and a longer term follow-up to achieve significant results. However, it would not be ethical to sustain long-term nonoperative treatment in symptomatic osteoarthritic patients with Kellgren-Lawrence grades 3 to 4. Second, the demographics of our patients might differ from those of patients who are candidates for HTO in Western countries. Most of our patients were female with a low BMI. The relatively old age, sex distribution of osteoarthritis, and low BMI (Table 1) are common findings in our ethnic group.¹⁶ These differences need to be considered to extrapolate our findings to other populations.

Third, the accuracy of the radiographic measurements is limited. The radiographic magnification and position of the knee joint could affect the minimal JSW and convergence angle. These influences could be minimized by the radiographic protocol of our center to standardize the position of the knee with the patella facing forward and an identical distance between the X-ray beam and cassette.⁵ Thus, we were able to obtain optimal radiographs and accurate digital measurements using the PACS in the present study. Fourth, the postoperative change in the PSA can also affect measurements of the minimal JSW and the convergence angle. However, we used navigation for CWHTO using a 4-pin guide technique and were able to minimize the unwanted change in the PSA by an accurate hinge location and symmetrical anterior and posterior wedge heights.⁴ We do not think that the minimal change of 0.8° in the mean PSA affected measurements of the minimal JSW and convergence angle in our patients. Lastly, although we used multiple, validated clinical scores to evaluate postoperative pain and function, those scales may not be sensitive enough to detect subtle changes arising from increased physical activities.²³ Therefore, the ceiling effect has to be considered to interpret the finding of the present study that there was no difference in clinical outcomes between the groups with an increased or decreased minimal JSW and convergence angle. Additional long-term survivorship analysis would be required to know whether the increase in the minimal JSW or no change in the convergence angle is a predictor of long-term clinical success in CWHTO.

Conclusion

The amount of cartilage healing, as indicated by the JSW, and clinical improvement were maintained until at least 3 years after CWHTO. Cartilage pressure, as indicated by the convergence angle, remained unchanged after CWHTO.

Footnotes

The authors declared that they have no conflicts of interest in the authorship and publication of this contribution.

References

Agneskirchner

Hurschler

Stukenborg-Colsman

Imhoff

Lobenhoffer

. Effect of high tibial flexion osteotomy on cartilage pressure and joint kinematics: a biomechanical study in human cadaveric knees. Winner of the AGA-DonJoy Award 2004. Arch Orthop Trauma Surg. 2004;124(9):575-584.

Agneskirchner

Hurschler

Wrann

Lobenhoffer

. The effects of valgus medial opening wedge high tibial osteotomy on articular cartilage pressure of the knee: a biomechanical study. Arthroscopy. 2007;23(8):852-861.

Aurich

Bedi

Smith

et al . Arthroscopic treatment of osteochondral lesions of the ankle with matrix-associated chondrocyte implantation: early clinical and magnetic resonance imaging results. Am J Sports Med. 2011;39(2):311-319.

Bae

Kim

Baek

Song

. Computer-assisted navigation decreases the change in the tibial posterior slope angle after closed-wedge high tibial osteotomy. Knee Surg Sports Traumatol Arthrosc. 2016;24(11):3433-3440.

Bae

Song

Kim

Seo

. Change in limb length after high tibial osteotomy using computer-assisted surgery: a comparative study of closed- and open-wedge osteotomies. Knee Surg Sports Traumatol Arthrosc. 2013;21(1):120-126.

Bae

Song

Kim

Hur

Jeong

. Mid-term survival analysis of closed wedge high tibial osteotomy: a comparative study of computer-assisted and conventional techniques. Knee. 2016;23(2):283-288.

Bae

Song

Yoon

. Closed-wedge high tibial osteotomy using computer-assisted surgery compared to the conventional technique. J Bone Joint Surg Br. 2009;91(9):1164-1171.

d’Entremont

McCormack

Agbanlog

et al . Cartilage health in high tibial osteotomy using dGEMRIC: relationships with joint kinematics. Knee. 2015;22(3):156-162.

Dettoni

Bonasia

Castoldi

Bruzzone

Blonna

Rossi

. High tibial osteotomy versus unicompartmental knee arthroplasty for medial compartment arthrosis of the knee: a review of the literature. Iowa Orthop J. 2010;30:131-140.

10.

Emrani

Katz

Kessler

et al . Joint space narrowing and Kellgren-Lawrence progression in knee osteoarthritis: an analytic literature synthesis. Osteoarthritis Cartilage. 2008;16(8):873-882.

11.

Gaasbeek

Nicolaas

Rijnberg

van Loon

van Kampen

. Correction accuracy and collateral laxity in open versus closed wedge high tibial osteotomy: a one-year randomised controlled study. Int Orthop. 2010;34(2):201-207.

12.

Herman

Giffin

. High tibial osteotomy in the ACL-deficient knee with medial compartment osteoarthritis. J Orthop Traumatol. 2016;17(3):277-285.

13.

Huizinga

Gorter

Demmer

Bierma-Zeinstra

Brouwer

. Progression of medial compartmental osteoarthritis 2-8 years after lateral closing-wedge high tibial osteotomy [published online July 7, 2016]. Knee Surg Sports Traumatol Arthrosc. doi:10.1007/s00167-016-4232-9.

14.

Kanamiya

Naito

Hara

Yoshimura

. The influences of biomechanical factors on cartilage regeneration after high tibial osteotomy for knees with medial compartment osteoarthritis: clinical and arthroscopic observations. Arthroscopy. 2002;18(7):725-729.

15.

Knutsen

Drogset

Engebretsen

et al . A randomized trial comparing autologous chondrocyte implantation with microfracture: findings at five years. J Bone Joint Surg Am. 2007;89(10):2105-2112.

16.

Koh

Kim

Chang

Cho

. Trends in use of total knee arthroplasty in Korea from 2001 to 2010. Clin Orthop Relat Res. 2013;471(5):1441-1450.

17.

Koshino

Murase

Saito

. Medial opening-wedge high tibial osteotomy with use of porous hydroxyapatite to treat medial compartment osteoarthritis of the knee. J Bone Joint Surg Am. 2003;85(1):78-85.

18.

Koshino

Wada

Ara

Saito

. Regeneration of degenerated articular cartilage after high tibial valgus osteotomy for medial compartmental osteoarthritis of the knee. Knee. 2003;10(3):229-236.

19.

Kumagai

Akamatsu

Kobayashi

Kusayama

Koshino

Saito

. Factors affecting cartilage repair after medial opening-wedge high tibial osteotomy. Knee Surg Sports Traumatol Arthrosc. 2017;25(3):779-784.

20.

Lee

Park

Han

. Effect of soft tissue laxity of the knee joint on limb alignment correction in open-wedge high tibial osteotomy. Knee Surg Sports Traumatol Arthrosc. 2016;24(12):3704-3712.

21.

Matsunaga

Akizuki

Takizawa

Yamazaki

Kuraishi

. Repair of articular cartilage and clinical outcome after osteotomy with microfracture or abrasion arthroplasty for medial gonarthrosis. Knee. 2007;14(6):465-471.

22.

Mina

Garrett

Jr Pietrobon

Glisson

Higgins

. High tibial osteotomy for unloading osteochondral defects in the medial compartment of the knee. Am J Sports Med. 2008;36(5):949-955.

23.

Lee

. A new high-flexion knee scoring system to eliminate the ceiling effect. Clin Orthop Relat Res. 2012;470(2):584-593.

24.

Ogawa

Matsumoto

Ogawa

Takeuchi

Akiyama

. Preoperative varus laxity correlates with overcorrection in medial opening wedge high tibial osteotomy. Arch Orthop Trauma Surg. 2016; 136(10):1337-1342.

25.

Bae

Yoon

Kim

. Analysis of knee joint line obliquity after high tibial osteotomy. J Knee Surg. 2016;29(3):649-657.

26.

Parker

Beatty

Giuffre

Scholes

Coolican

. Articular cartilage changes in patients with osteoarthritis after osteotomy. Am J Sports Med. 2011;39(5):1039-1045.

27.

Pavelka

Gatterova

Altman

. Radiographic progression of knee osteoarthritis in a Czech cohort. Clin Exp Rheumatol. 2000;18(4):473-477.

28.

Petersson

Boegard

Saxne

Silman

Svensson

. Radiographic osteoarthritis of the knee classified by the Ahlback and Kellgren & Lawrence systems for the tibiofemoral joint in people aged 35-54 years with chronic knee pain. Ann Rheum Dis. 1997;56(8):493-496.

29.

Rutgers

Bartels

Tsuchida

et al . dGEMRIC as a tool for measuring changes in cartilage quality following high tibial osteotomy: a feasibility study. Osteoarthritis Cartilage. 2012;20(10):1134-1141.

30.

Schaefer

Majewski

Hirschmann

Friederich

. Comparison of sagittal and frontal plane alignment after open- and closed-wedge osteotomy: a matched-pair analysis. J Int Med Res. 2008;36(5):1085-1093.

31.

Schroter

Ihle

Mueller

Lobenhoffer

Stockle

van Heerwaarden

. Digital planning of high tibial osteotomy: interrater reliability by using two different software. Knee Surg Sports Traumatol Arthrosc. 2013;21(1):189-196.

32.

Song

Bae

Kim

Lee

. Conversion total knee arthroplasty after failed high tibial osteotomy. Knee Surg Relat Res. 2016;28(2):89-98.

33.

Spahn

Kirschbaum

Kahl

. Factors that influence high tibial osteotomy results in patients with medial gonarthritis: a score to predict the results. Osteoarthritis Cartilage. 2006;14(2):190-195.

34.

Spahn

Klinger

Harth

Hofmann

. Cartilage regeneration after high tibial osteotomy: results of an arthroscopic study. Z Orthop Unfall. 2012;150(3):272-279.

35.

Terauchi

Shirakura

Katayama

Higuchi

Takagishi

Kimura

. Varus inclination of the distal femur and high tibial osteotomy. J Bone Joint Surg Br. 2002;84(2):223-226.

36.

Tsukada

Wakui

. Is overcorrection preferable for repair of degenerated articular cartilage after open-wedge high tibial osteotomy? Knee Surg Sports Traumatol Arthrosc. 2017;25(3):785-792.

37.

van der Woude

Wiegant

van Heerwaarden

et al . Knee joint distraction compared with high tibial osteotomy: a randomized controlled trial. Knee Surg Sports Traumatol Arthrosc. 2017;25(3):876-886.

38.

van Raaij

Takacs

Reijman

Verhaar

. Varus inclination of the proximal tibia or the distal femur does not influence high tibial osteotomy outcome. Knee Surg Sports Traumatol Arthrosc. 2009;17(4):390-395.

39.

Wakabayashi

Akizuki

Takizawa

Yasukawa

. A comparison of the healing potential of fibrillated cartilage versus eburnated bone in osteoarthritic knees after high tibial osteotomy: an arthroscopic study with 1-year follow-up. Arthroscopy. 2002;18(3):272-278.

40.

Wluka

Forbes

Wang

Hanna

Jones

Cicuttini

. Knee cartilage loss in symptomatic knee osteoarthritis over 4.5 years. Arthritis Res Ther. 2006;8(4):R90.