Superficial Medial Collateral Ligament Transection Sufficiently Increases Joint Space Width for Medial Meniscal Procedures During Medial Open-Wedge High Tibial Osteotomy

Abstract

Purpose

To investigate the changes in minimum joint space width (mJSW) caused by superficial medial collateral ligament (sMCL) transection during open-wedge high tibial osteotomy (OWHTO).

Methods

This study included consecutive patients with a diagnosis of medial unicompartmental knee osteoarthritis who were scheduled for OWHTO between September 2020 and August 2022. Intraoperative fluoroscopic evaluations of mJSW were performed under neutral, valgus stress, and varus stress positions in knee extension and 20° of flexion before sMCL transection, after transection, and after plate fixation. Changes in mJSW and increases in valgus stress were calculated and compared using analysis of variance. Linear regression analysis was performed to investigate the related factors for increased mJSW after transection.

Results

We included 44 knees in 43 patients in the final statistical analysis. The maximum mJSW occurred during valgus stress after sMCL transection at 20° of flexion and returned to baseline after plate fixation. Under the valgus stress condition, mean mJSW before transection was 5.1 ± 0.9 mm in extension and 5.5 ± 1.1 mm at 20° of flexion. It increased significantly after transection to 7.8 ± 1.4 mm (P < .001) and 9.2 ± 2.1 mm (P < .001), respectively. Regression analysis showed that increased mJSW after transection in extension positively correlated with the knee extension angle (P = .032). Overall, mJSW increased with sMCL transection regardless of the preoperative condition.

Conclusions

Transection of the sMCL in OWHTO effectively enlarged the mJSW to 9.2 mm, which was 3.8 mm greater than that before transection, facilitating medial meniscal procedures. After plate fixation, the mJSW returned to pre-transection levels.

Level of Evidence

Level Ⅳ, therapeutic case series.

High tibial osteotomy is an established treatment for medial unicompartmental knee osteoarthritis (OA), especially in the early phase.1, 2, 3 It aims to shift the mechanical axis from the medial side to slightly lateral to the knee midline, reducing load and delaying OA progression. However, managing a degenerative medial meniscus, especially a medial meniscal posterior root tear (MMPRT), during open-wedge high tibial osteotomy (OWHTO) lacks a defined strategy. Repairing the medial meniscus during OWHTO can restore meniscal function and reduce femorotibial contact pressure, which increases by 180% with an MMPRT.⁴ Although treating the MMPRT is crucial, caution is necessary for the meniscus’s posterior portion owing to narrowed medial joint space in osteoarthritic knees, which is a known risk factor for iatrogenic chondral damage.⁵

Occasionally, the “pie-crusting” technique for the medial collateral ligament (MCL) is needed to widen the medial joint space.5, 6, 7, 8, 9 Despite widening the space, this technique comes with potential risks, such as mild postoperative pain at the release site, saphenous nerve and vein damage, and increased risk of iatrogenic MCL injury.¹⁰

Alternatively, OWHTO often involves transecting or releasing the superficial medial collateral ligament (sMCL), which is the primary restraint against knee valgus.11, 12, 13, 14 Previous biomechanical studies showed a significant increase in displacement when valgus stress was applied after sMCL transection.¹⁵ If sMCL transection provides sufficient joint space widening, comparable to the pie-crusting technique, it could be less invasive and beneficial for patients. However, whether sMCL transection effectively widens the medial joint space for meniscal repair—or to what extent—is unclear.

The purpose of this study was to investigate the changes in minimum joint space width (mJSW) caused by sMCL transection during OWHTO. We hypothesized that sMCL transection alone would provide sufficient additional mJSW for safe posterior medial meniscal repair, eliminating the need for the pie-crusting technique.

Methods

Patients

Consecutive patients who met the following inclusion criteria were retrospectively identified: diagnosis of medial unicompartmental knee OA and scheduled to undergo OWHTO between September 2020 and August 2022. The exclusion criteria were as follows: lateral knee OA with valgus deformity; severe patellofemoral joint OA; inflammation including rheumatoid or psoriatic arthritis; anterior cruciate ligament deficiency; tibial, femoral, or other lower-extremity joint deformities; varus deformity with Blount disease; postoperative open fracture of knee joint; and incomplete medical data. Demographic data (age, sex, and body mass index [BMI]) of all patients at the time of surgery were collected from medical records. All patients provided written informed consent, and the study was approved by the ethics committee of our institute.

Surgical Procedure

Before surgery, postoperative lower-limb alignment was targeted at the weight-bearing line to pass through the Fujisawa point, which is 62.5% of the width of the tibial plateau relative to the medial end.^16,17 Planning was conducted using digital planning software (MediCAD; Hectec, Landshut, Germany) on anteroposterior full–weight-bearing whole-leg radiographs.

Before OWHTO, an arthroscopic evaluation was performed to assess the condition of the articular cartilage, meniscus, and cruciate ligaments. A longitudinal skin incision was made to the medial aspect of the proximal tibia, and the pes anserinus was identified. The first layer was incised along with the pes anserinus and retracted posteriorly using radiolucent retractors (Fig 1A). Then, the level of osteotomy was determined by fluoroscopy, and the exposed sMCL was transected using chisels and knives (Fig 1 B and C). After sMCL transection, medial meniscal procedures were performed if necessary.

Fig 1.

Superficial medial collateral ligament (sMCL) transection during surgery. (A) On the medial side of the left knee, the first layer was incised along with the proximal pes anserinus (asterisk) and retracted posteriorly using radiolucent retractors, and the sMCL was identified (triangles). (B) The level of osteotomy was determined using fluoroscopy. (C) Transection of the sMCL was performed using chisels.

All OWHTO procedures were performed with the TriS Medial HTO Plate System (Olympus, Tokyo, Japan). The monoplane or biplane osteotomy was performed, and opening of the proximal tibia was performed. The amount of opening gap was determined by the weight-bearing line ratio using an alignment rod from the center of the femoral head and talus under fluoroscopic guidance. A wedged β-tricalcium phosphate block was placed on the posterior of the opening gap space. Finally, the proximal tibia was fixed to each plate.

Intraoperative Fluoroscopic Evaluation

Intraoperative fluoroscopic evaluations were performed in 3 positions: neutral, valgus stress, and varus stress in knee extension and 20° of flexion (Fig 2). For the valgus and varus stress tests, the surgeon (E.S., T.T., S.S., and D.C.) manually applied maximum stress for each position during separate capture series. These 3 captures were recorded before sMCL transection, after sMCL transection, and after plate fixation. All captures were calibrated with a 4-mm-diameter cylindrical alignment rod, and the captured data were saved as PDF files.

Fig 2.

Intraoperative measurements of minimum joint space width. Fluoroscopic views of the left knee are shown. Minimum joint space width in the neutral condition (A), valgus stress condition (B), and varus stress condition (C) was measured before transection (D), after transection (E), and after plate fixation (F). Each capture was recorded in both extension and 20° of flexion.

The mJSW was defined as the minimal tangential distance from the proximal tibial plateau line connecting the medial and lateral bony end of the proximal tibia, and was measured according to the method reported by Han et al.⁷ (Fig 3). For each capture, the minimum joint space width was measured using ImageJ software (National Institutes of Health, Bethesda, MD) and standardized with the width of the alignment rod.

Fig 3.

Intraoperative measurement of minimum joint space width in left knee. Minimum joint space width was defined as the minimum tangential distance from the proximal tibia plateau line (A) to the medial femoral condyle (B).

Statistical Analysis

Demographic data were presented as mean ± standard deviation, and group comparisons (demographic data of men vs women) were performed using the χ² test for categorical variables and the Mann-Whitney U test for continuous variables. The mJSW values were shown as mean ± standard deviation and 95% confidence interval, and the changes during surgery were compared using 2-way analysis of variance and the Tukey post hoc test. The increase in mJSW was calculated as the difference between mJSW under valgus stress and mJSW in the neutral position. In addition, the increasing ratio was calculated as an increase in the mJSW divided by the mJSW in the neutral position.

Linear regression analysis was performed to identify factors related to the maximum mJSW and the mJSW increase after sMCL transection. Dependent variables included mJSW under valgus stress after sMCL transection and increased mJSW with sMCL transection. Independent variables included age, sex, BMI, knee extension and flexion angles, mJSW in neutral position at extension, and increased mJSW with valgus stress. Data input and analysis were performed using SPSS software (version 27.0; IBM, Armonk, NY). The level of statistical significance was set at P < .05.

Results

Demographic Data

This study included 44 knees in 43 patients, including 11 knees in men and 33 knees in women, for the statistical analysis. The mean age (± standard deviation) was 62.3 ± 6.5 years in men and 58.9 ± 8.3 years in women. The mean BMI was 27.3 ± 2.9 in men and 26.3 ± 3.9 in women. The mean knee extension and flexion angles were –4.6° ± 3.5° and 139.1° ± 10.4°, respectively, in men and –3.0 ± 3.4° and 137.3° ± 11.4°, respectively, in women.

Intraoperative Measurements of mJSW

Regarding the overall mJSW changes during surgery, mJSW increased in the valgus stress condition before transection, after transection, and after plate fixation in both extension (P < .001) and 20° of flexion (P < .001) (Table 1, Fig 4). The maximum mJSW was observed in the valgus stress condition after sMCL transection.

Table 1.

Intraoperative Measurements of mJSW

	Intraoperative mJSW, mm
	Before Transection			After Transection			After Plate Fixation
	Neutral	Valgus Stress	Varus Stress	Neutral	Valgus Stress	Varus Stress	Neutral	Valgus Stress	Varus Stress
Extension	3.6 ± 1.0 (3.2-3.9)	5.1 ± 0.9 (4.8-5.3)	3.3 ± 0.9 (3.0-3.5)	3.7 ± 1.0 (3.3-4.0)	7.8 ± 1.4 (7.3-8.2)	3.2 ± 0.9 (2.9-3.5)	3.4 ± 1.0 (3.1-3.7)	4.9 ± 1.1 (4.5-5.2)	3.0 ± 0.9 (2.8-3.3)
20° of flexion	3.3 ± 1.0 (3.0-3.6)	5.5 ± 1.1 (5.1-5.8)	2.9 ± 1.1 (2.6-3.3)	3.5 ± 1.1 (3.2-3.8)	9.2 ± 2.1 (8.8-9.9)	2.8 ± 1.0 (2.5-3.1)	3.0 ± 1.2 (2.6-3.4)	5.2 ± 1.1 (4.8-5.6)	2.6 ± 1.0 (2.3-2.9)

NOTE. Data are presented as mean ± standard deviation (95% confidence interval) in neutral position, under valgus stress, and under varus stress. Intraoperative mJSW was measured before superficial medial collateral ligament transection, after transection, and after plate fixation.

mJSW, minimum joint space width.

Fig 4.

Changes in minimum joint space width (mJSW) during surgery. Box plot graphs of mJSW in knee extension (A) and 20° of flexion (B) are shown. The boxes indicate the first and third quartiles; bars, maximum and minimum values; and dots, outliers for each condition.

Increases in mJSW Under Valgus Stress

In the valgus stress condition, although mean mJSW was 5.1 ± 0.9 mm in extension and 5.5 ± 1.1 mm in 20° of flexion before sMCL transection, these values increased to 7.8 ± 1.4 mm (P < .001) and 9.2 ± 2.1 mm (P < .001), respectively, after sMCL transection (Table 1). Additionally, these increases returned to the baseline values of 4.9 ± 1.1 mm and 5.2 ± 1.1 mm, respectively, after plate fixation, similar to those of pre-sMCL transection in extension (P = .748) and 20° of flexion (P = .721). The changes in mJSW with valgus stress in extension and 20° of flexion were 4.1 ± 1.4 mm (P < .001) and 5.7 ± 2.4 mm (P < .001), respectively, compared with values of 1.5 ± 1.1 mm and 2.2 ± 0.9 mm, respectively, before sMCL transection (Table 2). Notably, sMCL transection could obtain 2.7 ± 1.5 mm of additional mJSW in extension and 3.5 ± 2.3 mm in 20° of flexion. The increasing ratios were 227.4% and 281.2% for extension and 20° of flexion, respectively (Table 2). The increasing ratio after plate fixation returned to the same level as before sMCL transection in both extension and 20° of flexion (P = .543) (Table 2).

Table 2.

Increases in mJSW Under Valgus Stress

	Before Transection		After Transection		After Plate Fixation
	Increase in mJSW, mm	Increasing Ratio, %	Increase in mJSW, mm	Increasing Ratio, %	Increase in mJSW, mm	Increasing Ratio, %
Extension	1.5 ± 1.1	153.4 ± 48.6	4.1 ± 1.4∗	227.4 ± 66.5	1.5 ± 1.0	152.8 ± 48.9
20° of flexion	2.2 ± 0.9	175.5 ± 39.8	5.7 ± 2.4∗	281.2 ± 81.6	2.2 ± 1.3	199.8 ± 97.7

NOTE. Data are presented as mean ± standard deviation. The amount of increase and increasing ratio of mJSW by valgus stress were measured before transection, after transection, and after plate fixation. Increases in mJSW were compared using analysis of variance and the Tukey test. The level of statistical significance was set at P < .05 and was compared before transection and after transection.

mJSW, minimum joint space width.

^∗Statistically significant (P < .05).

Related Factors for mJSW After sMCL Transection

In the extension position, the mJSW under valgus stress after sMCL transection was positively correlated with the knee extension angle (P = .032) (Table 3). In addition, the increase in mJSW with sMCL transection was positively correlated with the knee extension angle (P = .010). Conversely, in 20° of flexion, no significant related factors were observed for the mJSW, which increased with sMCL transection (Table 3).

Table 3.

Related Factors for mJSW after sMCL Transection and Increased mJSW With sMCL Transection

	mJSW After sMCL Transection				Increased mJSW With sMCL Transection
	Extension		20° of Flexion		Extension		20° of Flexion
	β	P Value	β	P Value	β	P Value	β	P Value
Age	0.12	.491	0.41∗	.020∗	0.01	.953	0.24	.200
Women	–0.19	.246	–0.21	.204	–0.12	.434	–0.06	.743
Body mass index	–0.04	.818	0.01	.980	–0.14	.372	0.09	.652
Knee extension angle	0.40∗	.032∗	0.10	.593	0.44∗	.010∗	0.20	.324
Knee flexion angle	–0.12	.478	–0.14	.388	–0.08	.609	–0.15	.415
mJSW in neutral position	0.39	.089	0.18	.391	–0.19	.332	0.13	.575
Increased mJSW with valgus stress	0.22	.327	–0.09	.662	–0.67	.002	–0.22	.357

NOTE. Linear regression analysis was performed with mJSW under the valgus stress condition after sMCL transection and increased mJSW with sMCL transection as the dependent variables. Age, sex, body mass index, knee extension and flexion angles, mJSW in the neutral position in extension, and increased mJSW with valgus stress were the independent variables.

mJSW, minimum joint space width; sMCL, superficial medial collateral ligament.

^∗Statistically significant (P < .05).

Discussion

The main finding of this study is that sMCL transection during OWHTO significantly widened the mJSW, providing an additional 2.7 ± 1.5 mm in extension and 3.5 ± 2.3 mm in 20° of flexion. The increase in mJSW was primarily influenced by flexion contracture only in the extended position of the knee. In contrast, the maximum mJSW and the amount of increased mJSW with sMCL transection were remarkably increased regardless of other preoperative conditions. These results indicate that sMCL transection effectively widens the mJSW, particularly in 20° of flexion, facilitating safe posterior medial meniscal repair in OWHTO.

Various suturing techniques and devices for medial meniscal repair have recently been reported. However, treatment of the posterior portion of the medial meniscus, especially for an MMPRT,¹⁸ remains challenging, even in OWHTO cases,¹⁹ because the mJSW is narrow in knees with medial compartment OA. A suture passer with sufficient mJSW is required to avoid iatrogenic cartilage damage. The thickness of the suture passer commonly used for MMPRT repair ranges from 3 to 5 mm. In our study, the 95% confidence interval of the mJSW under valgus stress in 20° of flexion was 8.8 mm, a sufficient width for using the suture passer, even accounting for cartilage thickness. Considering that the mJSW under valgus stress did not reach 5 mm before sMCL transection in half of the cases, sMCL transection was useful when using suture passers in OWHTO cases with challenging posterior medial meniscal tears.

Biomechanical studies have revealed that sMCL injuries widen the gap by approximately 13.2 mm during extension and 15 mm during 20° of flexion.¹⁵ Compared with the pie-crusting technique, sMCL transection is considered an effective and reasonable treatment during OWHTO. The pie-crusting technique widens the mJSW by 3.2 ± 0.6 mm (range, 2.0-4.4 mm).⁷ However, this technique should be avoided if possible because of the potential risk of mild postoperative pain at the site of release, as well as damage to the saphenous nerve and greater saphenous vein, and the possibility of iatrogenic grade 1 MCL injury.¹⁰ Therefore, sMCL transection is a safer, simpler, and more effective approach for joint space widening in OWHTO than the pie-crusting technique, particularly considering its superior widening capacity.

Previously, Pape et al.¹⁴ suggested that the sMCL was not completely released during OWHTO. Focusing on OWHTO cases, caution should be exercised when performing transverse osteotomy closer to the tibial plateau with sMCL release during OWHTO because it is associated with greater valgus joint laxity postoperatively.²⁰ However, Sato et al.²¹ proved that the sMCL was histologically healed 1 year after OWHTO, and good stability was obtained, even when the sMCL was completely released. This study revealed that plate fixation with the remaining pes anserinus effectively restored time-zero stability against valgus stress, even after sMCL transection. Kim et al.²² reported no valgus instability 2 years after surgery. Furthermore, a systematic review showed that radiographic medial joint space widening was only 0 to 1.1 mm at 24 months after surgery.⁸ Therefore, although caution is always warranted, sMCL transection appears to be a safe and effective method for joint space widening in OWHTO without compromising long-term stability.

This study shows that sMCL transection during OWHTO effectively enlarged the mJSW, achieving a significant increase of 3.8 mm compared with pre-transection values. This expanded space, reaching a post-transection maximum of 9.2 mm, provides sufficient access for safe and efficient medial meniscal repair procedures. Notably, plate fixation effectively restored the mJSW to its pre-transection level, ensuring long-term joint stability. These findings suggest that sMCL transection presents a valuable strategy for facilitating posterior medial meniscal repair in OWHTO while maintaining joint stability. Although this study provides promising evidence for sMCL transection as a joint space–widening technique in OWHTO, further research is warranted to refine our understanding and optimize its clinical application.

Limitations

This study has several limitations beyond its time-zero study design. First, it was a case-series study, which limits the ability to draw definitive conclusions. Second, the statistical analysis was not performed in men and women separately owing to the insufficient number of enrolled patients. Third, postoperative instability was not confirmed. Finally, the study did not include postoperative functional tests and patient-reported outcome measures, which limits the comprehensiveness of the assessment.

Conclusions

Transection of the sMCL in OWHTO effectively enlarged the mJSW to 9.2 mm, which was 3.8 mm greater than that before transection, facilitating medial meniscal procedures. After plate fixation, the mJSW returned to pre-transection levels.

Disclosures

All authors (E.S., T.T., Y.K., Y.S., S.S., D.C., Y.I.) declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.