Purpose
To evaluate the association between arthroscopically detected lateral meniscus (LM) hypermobility and popliteomeniscal fascicle (PMF) injuries in patients with varus knee osteoarthritis undergoing medial opening-wedge high tibial osteotomy (MOWHTO).
Methods
Patients with varus knee osteoarthritis who underwent MOWHTO were retrospectively reviewed. During arthroscopic observation before osteotomy, the presence of LM hypermobility and PMF tears was assessed. Tom’s test was performed under standardized negative pressure using an arthroscopic suction system. LM hypermobility was defined as complete posterior translation of the LM beyond the midpoint of the lateral tibial plateau without major tear. The association between LM hypermobility and PMF tear was analyzed using logistic regression.
Results
LM hypermobility was detected in 72 of 136 knees. PMF tears were observed in 65 knees. LM hypermobility was significantly associated with PMF tears. Among the entire cohort, 33 knees had partial-type discoid lateral meniscus (DLM), and 3 knees had complete-type DLM. Among the hypermobile LM group, 21 knees presented with partial or complete DLM, whereas only 15 knees in the stable LM group had DLM. However, this difference was not statistically significant. Demographic characteristics including age, body mass index, preoperative mechanical axis, and Kellgren-Lawrence grade were comparable between the LM hypermobile and stable groups. No significant differences in clinical symptoms related to the lateral compartment were observed between groups.
Conclusions
LM hypermobility is a frequent arthroscopic finding in patients undergoing MOWHTO and is significantly associated with PMF tears. Despite the absence of preoperative lateral symptoms, LM instability may represent a relevant intraoperative consideration.
Level of Evidence
Level IV, retrospective case series.
Medial opening-wedge high tibial osteotomy (MOWHTO) is a well-established surgical option for patients with medial compartment osteoarthritis of the knee, especially among active and relatively younger individuals. However, in elderly patients, unicompartmental knee arthroplasty may be favored, depending on region and surgical preference.
Recent studies have highlighted the importance of recognizing lateral meniscus (LM) pathology, ,, particularly in the setting of medial realignment procedures. Among these, LM hypermobility has gained interest because of its potential role in postoperative lateral compartment overload. LM hypermobility is generally defined as excessive posterior translation of the LM without a major tear, and it is considered rare in the general population.
Discoid lateral meniscus (DLM) and popliteomeniscal fascicle (PMF) injuries are potential contributors to LM hypermobility. , DLM is a known risk factor for LM tears and is regarded as a relative contraindication for MOWHTO because of increased risk of postoperative lateral degeneration. However, the clinical relevance of arthroscopically detected LM hypermobility in patients without lateral symptoms remains unclear. The purpose of this study was to evaluate the association between arthroscopically detected LM hypermobility and PMF injuries in patients with varus knee osteoarthritis undergoing MOWHTO.
Methods
This retrospective study included 136 patients who underwent MOWHTO between January 2019 and December 2022. Patients with a history of previous lateral meniscal surgery, concomitant cruciate ligament reconstruction, valgus deformity, or those undergoing double-level osteotomy were excluded. All procedures were performed by 1 experienced orthopaedic surgeon (T.T.) at a single academic center and 3 affiliated hospitals. This study was conducted in accordance with the Declaration of Helsinki and was approved by the Ishibashi General Hospital Ethics Committee for Medical Research (Approval ID:25-009). This was a retrospective study. All patients received standard treatment, and the requirement for informed consent from individual participants was waived.
Preoperative imaging included standing long-leg radiographs and magnetic resonance imaging, which were used to evaluate limb alignment and meniscal morphology, including the presence of DLM. DLM was categorized as complete or partial type on the basis of magnetic resonance imaging and intraoperative findings. Radiographic evaluation included Kellgren-Lawrence (KL) grade, hip-knee angle, medial proximal tibial angle, and posterior tibial inclination, measured by 2 observers with interobserver reliability >0.80.
MOWHTO was performed using neutral alignment techniques. ,, Arthroscopic examination using a 45° scope was conducted immediately before osteotomy ( Fig 1 ). Evaluation of the LM was performed first, followed by PMF assessment in a standardized sequence. ,, LM hypermobility was assessed using Tom’s test under standardized negative pressure applied via an arthroscopic suction system ( Fig 2 ). Suction was standardized to 100 mm Hg. Hypermobility was defined as posterior translation of the entire LM beyond the midpoint of the lateral tibial plateau without a major tear. Cases with lack of an obvious tear but persistent mobility were classified as hypermobile. PMF tears were evaluated arthroscopically by probing the LM and visualizing disruption or discontinuity of the fascicular fibers on the popliteal hiatus. The presence or absence of PMF tears was recorded.
Comparison of arthroscopic views of the popliteal tendon and intact and torn anterior (aPMF), posterosuperior (psPMF), and posteroinferior popliteomeniscal fascicles (piPMF) of the left knee. (PT, popliteal tendon.)
Arthroscopic view of the extruded lateral meniscus of the left knee during Tom’s test. (LFC, lateral femoral condyle,; LM, lateral meniscus; LTP, lateral transpsoas.)
When LM hypermobility or PMF tear was identified, the meniscus was inspected for further pathology; however, no meniscal repair or partial meniscectomy was performed in asymptomatic patients. LM repair was performed using an all-inside technique in symptomatic cases. Clinical data collected included age, sex, body mass index, KL grade, preoperative alignment, and range of motion. Patients with KL grade 1 were included only if they met early knee osteoarthritis criteria.
Statistical Analysis
Data were analyzed using EZR software. Variables were tested for normality and presented as mean ± standard deviation. Categorical data were analyzed using the Fisher exact test. Logistic regression was performed to identify factors associated with LM hypermobility. Predictor selection was guided by Bayesian information criterion.
Results
Patient Demographics
A total of 136 patients were included in the analysis (50 male and 86 female), with a mean age of 63.6 ± 9.8 years. The average height and weight were 1.61 ± 0.09 m and 65.5 ± 13.7 kg, respectively, resulting in a mean body mass index of 25.2 ± 4.0. The preoperative maximum flexion angle of the knee was 127.5° ± 11.0° ( Table 1 ).
Table 1
Demographic Characteristics
| Variables | N = 136 |
|---|---|
| Mean ± SD | |
| Age, yr | 63.5 ± 9.8 |
| Sex (female) | 86 (63.2%) |
| Affected side (right knee) | 59 (43.4%) |
| Height, m | 1.61 ± 0.09 |
| Weight, kg | 65.5 ± 13.7 |
| Body mass index | 25.2 ± 4.0 |
| Preoperative range of motion for flexion, ° | 127.5 ± 11.0 |
| Kellgren-Lawrence classification (grade 1/2/3/4) | 20/75/36/5 |
| Preoperative hip-knee angle, ° | 4.5 ± 2.4 |
| Preoperative medial proximal tibial angle, ° | 84.9 ± 7.3 |
| Preoperative posterior tibial inclination, ° | 10.8 ± 10.9 |
SD, standard deviation.
Radiographic Findings
The KL grade revealed 20 patients with grade 1, 75 with grade 2, 36 with grade 3, and 5 with grade 4 osteoarthritis. The mean preoperative hip-knee angle was 4.5° ± 2.4° (positive values indicating varus alignment). The medial proximal tibial angle was 84.9° ± 7.3°, and the posterior tibial inclination was 10.8° ± 10.9° ( Table 1 ).
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