Effect of tibial rotation after uniplane medial open-wedge high tibial osteotomy in genu varum patients: An observational study

Abstract

The change in axial tibial rotation after uniplane medial open-wedge high tibial osteotomy (uniplane OWHTO) and its relevant influence factor is not known. Therefore, the aim of this study was to evaluate the change in axial tibial rotation after uniplane OWHTO, and the factors affecting tibia rotational change were analyzed. Between January 2022 and April 2022, the study was retrospectively conducted on genu varum patients who underwent uniplane OWHTO. In the weight-bearing anteroposterior long leg view, the hip-knee-ankle angle and medial proximal tibial angle (MPTA) were evaluated. The posterior tibial slope were measured from the lateral view. A CT scan of the knee joint was performed to evaluate the distal tibial rotation angle (TRA), femorotibial rotation angle and tibial tuberosity-trochlear groove distance. In addition, the foot morphology was assessed by the ankle deformity angle and ankle rotation angle using an angle measuring instrument. All parameters were measured preoperatively and 14 days after surgery. The mean change in hip-knee-ankle, MPTA was 10.5°±2.9°, 8.8°±2.6°. The mean preoperative and postoperative TRA were 25.1°±6.9° and 22.2°±6.2° respectively (P = .007). Thus, the mean ∆TRA was −3.0°±3.4° (IR) with a range of −9.6° to +2.8° after surgery. No significant differences were found in the femorotibial rotation angle and tibial tuberosity-trochlear groove distance before and after surgery (P > .05). The postoperative ankle rotation angle and ankle deformity angle changed significantly compared with preoperative values (P < .001). In the multiple regression analysis, ∆MPTA was the only predictor of distal tibial rotation (β = 0.667, P = .003). The current study confirms an unintended internal rotation in the distal tibia following uniplane MOWHTO and the rotation in the distal tibia was influenced by the opening width. Surgeron should keep in mind to avoid the osteotomy complication leading to excessive rotation change during surgery.

1. Introduction

High tibial osteotomy (HTO) has become a minimally invasive and effective treatment for osteoarthritis in the medial compartment of the knee.^[1] By transferring the weight-bearing line from the degenerative medial compartment to the intact lateral compartment, this relieves joint pain and prevents degeneration in the medial knee.^[2] With continuous improvement in surgical techniques, satisfactory mid- and long-term outcomes have been reported after HTO.^[3,4]

As is known, it is very important to obtain accurate alignment correction during surgery.^[5] Previous studies mostly focused on changes of the sagittal plane and coronal plane in the proximal tibia.^[6,7] However, the proximal tibia is a three-dimensional structure that can be visualized along the coronal, sagittal, and axial planes. The distal tibial rotation is an important and easily overlooked factor affecting the knee kinematics, contact forces and overall gait of patients with osteoarthritis in axial planes, but has not been well studied.^[8–10] In recent years, several studies have suggested that unexpected rotational change of the distal tibia occurs after biplane medial open-wedge HTO (biplane OWHTO) and lateral closing-wedge HTO (CWHTO).^[11,12] Subsequently, other research has also tried to explain the mechanism of postoperative axial tibial rotation and evaluate the factors affecting tibial rotational change, including the direction of vertical osteotomy, the magnitude of the osteotomy gap (OW) and hinge instability after biplane OWHTO and CWHTO.^[13,14] However, uniplane OWHTO is a different surgical technique performed from the distal third of the tibial tuberosity,^[15] so the tibial rotation and relevant influencing factors might differ from previous research. To our knowledge, there have been no studies evaluating the change in axial tibial rotation and the factors influencing tibial rotation following uniplane OWHTO.

Therefore, the aim of this study was to assess the change in axial tibial rotation after uniplane OWHTO and to analyze the factors affecting tibial rotational change. We hypothesize that unintended internal rotational changes occur in the distal tibial. In addition, we hypothesize that the osteotomy gap magnitude during uniplane OWHTO is associated with the distal tibial axial rotation.

2. Materials and methods

2.1. inclusion and exclusion criteria

Between January 2022 and April 2022, the research study was retrospectively conducted on 41 knees from 35 patients who underwent uniplane MOWHTO. The patients were excluded according to the following criteria from the study: Patients lacking complete imaging data (n = 2); those with surgery-related complications, including limitation of joint movement or surgical incision infection (n = 1). The patients who do not receive the same rehabilitation protocol after surgery^[16] (n = 0). The patients lost to follow-up at the final evaluation (n = 1). Finally, 4 patients (4 knees) were excluded and 31 patients (37 knees) were included in this study. The inclusion criteria for surgery were medial unicompartmental osteoarthritis; medial proximal tibial angle < 85°, normal mechanical lateral distal femur angle (87 ± 3°), varus deformity ≥ 5°; Kellgren-Lawrence grade ≥ II^[17]; the age of patients ≤ 65 years; and body mass index (BMI) ≤ 35 kg/m². Exclusion criteria for surgery were: previous history of knee or ankle surgery; limited knee motion ≤ 100° or flexion deformity > 10°; rheumatic arthritis or other inflammatory arthropathy; symptomatic OA of the lateral compartment^[18]; or ligamentous laxity around the knee and ankle. All operations were performed by the same senior surgeon. The study was approved by the institutional review board of our hospital (2020bkkyLW005) and written informed consent was obtained from all participants before surgery.

2.2. Surgical procedure and rehabilitation

At the start, a knee arthroscopy was performed to debride the joint cavity and degenerated cartilage when necessary. Then, an incision of about 5 cm was made in the proximal medial tibia, partially releasing the pes anserinus tendon and the superficial layer of the medial collateral ligament (sMCL). A Homann hook was inserted in the posterior tibial margin to protect the nerve and blood vessels. The osteotomy site from the distal third of the tibial tuberosity to the fibular head was marked using 2 Kirschner wires. The osteotomy procedure was performed using an oscillating saw and bone chisel and located 10 mm laterally from the hinge. The hinge was weakened by the Kirschner wire used to drill the lateral cortex. The assistants compressed the patella to maintain a straight knee and everted the foot to relieve tension in the tibialis anterior muscle. Another assistant everted the tibia to open the osteotomy gap towards to the WBL ratio of 62% according to the preoperative plan. A π plate (Shuangyang, China) was used to fix the osteotomy site in the medial tibia. The cancellous bone chips and bone morphogenetic protein (BMP) were used to fill the osteotomy gap and one drainage tube was placed in the incision. After closing the incision, the elastic pressure dressing bandage was used to relieve postoperative knee joint swelling.

The postoperative rehabilitation protocol was the consistent with the early full-weight-bearing protocol proposed by Takeuchi et al.^[16] Quadriceps femoris isometric contraction training was performed 1 day after surgery. After removing the drainage tube, continuous passive motion exercise should be used to promote the restoration of knee joint movement. With the help of a walker, partial weight bearing on the knee joint was permitted after 1 week. A gradual increase in weight bearing was allowed within 4 weeks for progressive recovery. Full weight-bearing training was permitted at 4 weeks postoperatively.

2.3. Radiographic evaluation

In the weight-bearing anteroposterior long leg view (Fig. 1), the patella should be located in front of the center of the femoral condyle. The hip-knee-ankle (HKA) angle was used to indicate the mechanical axis change. This was done using 2 lines drawn from the center of the femoral head to the midpoint of the articular surface line in the distal femur and the midpoint of the tibial plateau to the midpoint of the ankle joint (∠α). The medial proximal tibial angle (MPTA) was defined as the medial angle between the tibial plateau tangent and a line perpendicular to the mechanical axis of the tibial shaft (∠β). In the lateral view, the position of the knee joint was maintained at 30 degrees flexion. The posterior tibial slope (PTS) was defined as the angle between the tibial plateau tangent and a line perpendicular to the anatomical axis of the proximal tibia shaft (90°−∠γ). The change (∆) in HKA, MPTA, PTS represent the differences between postoperative and preoperative values. ∆MPTA indicated the osteotomy gap (OW) magnitude during HTO. The negative HKA value indicated varus of lower limbs, while positive HKA values indicated valgus of lower limbs. All the radiographic data were evaluated before and 14 days after surgery.

Figure 1.

Measuring the angle after uniplane OWHTO using CT scans. L1, the proximal posterior tibial rim; L2, the transmalleolar axis; L3, the posterior condylar line of the distal femur; L4, the perpendicular line from the deepest point of the femoral trochlear groove to the posterior condylar line of the distal femur; L5, the perpendicular line from the midpoint in the anterior aspect of tibial tuberosity to L1; The distal TRA indicated the angle between L1 and L2; The TT-TG indicated the distance (e) between L4 and L5. TRA = distal tibial rotation angle, TT-TG = tibial tuberosity-trochlear groove distance, Uniplane OWHTO = uniplane medial open-wedge high tibial osteotomy.

In the CT scan, a helical CT (Philips-705 Mecical Systems, Royal Dutch Philips Electronics Ltd., Amsterdam, Netherlands) was used and all CT data was obtained via a knee-ankle CT scan in 1-mm slices (Fig. 2). As is commonly known, tibial rotational change can be affected by femoral and ankle rotation, so the lower limbs of patients had a neutral patella position so as to straighten the knee, relax the ankle joint and maintain an immobile lower limb. The tibial rotational change was performed using 3 slices, with the first being the proximal posterior tibia layer above the tibial tuberosity (A). The second was the distal tibial malleolus layer tangent to the talar dome (B). The third was the distal femoral condylar layer at the most prominent layer of the medial-lateral condyle (C). The distal tibial rotation angle (TRA) was defined as the angle between the proximal posterior tibial rim (L1) and the transmalleolar axis (L2). The femorotibial rotation angle (FTRA) was defined as the angle between the posterior condylar line of the distal femur (L3) and proximal posterior tibial rim (L1). Tibial tuberosity-trochlear groove distancing (TT-TG) was performed using 2 slices. The first was the deepest layer of the femoral trochlear groove (C), followed by the most prominent layer in the anterior aspect of tibial tuberosity (D). In the first stage, L4 was the perpendicular line from the deepest point of the femoral trochlear groove to the posterior condylar line of the distal femur (L3); In the second slice, L5 was the perpendicular line from the midpoint in the anterior aspect of the tibial tuberosity to the posterior tibial rim (L3). The TT-TG was defined as the distance (E) between L4 and L5. The changes (∆) in TRA, FTRA, and TT-TG represent the differences between postoperative and preoperative values. For TRA changes, internal rotation (IR) in the distal tibia is represented by a negative value and external rotation (ER) is represented by a positive value. For FTRA changes, ER in the femur is indicated by a positive value and IR is indicated by a negative value. All the CT data were evaluated before and 14 days after surgery.

Figure 2.

Measuring the angle after uniplane OWHTO using plain film radiographs. A, HKA (∠α); B, MPTA (∠β); C, PTS (90°−∠γ); D, a π plate used in the uniplane OWHTO. HKA angle = hip-knee-ankle angle, MPTA = medial proximal tibial angle, PTS = posterior tibial slope, Uniplane OWHTO = uniplane medial open-wedge high tibial osteotomy.

In addition, foot morphology was evaluated before and 14 days after surgery using the angle measuring instrument (Fig. 3). The ankle deformity angle (ADA) in the coronal plane was defined as the angle between the knee-ankle midpoint line (L1) and the long dorsum pedis axis (L2). The ankle rotation angle (ARA) in the axial plane was defined as the angle between the long planta pedis axis (L3) and a line perpendicular (L5) to the horizontal plane (L4). The change (∆) in ADA and ARA represent the differences between postoperative and preoperative values. A negative value indicated varus of the ankle (ADA) and IR of the ankle (ARA), while a positive value indicated valgus of the ankle (ADA) and ER of the ankle (ARA).

Figure 3.

Measuring the foot morphology before and after uniplane OWHTO. A, ADA (∠δ) was defined as the angle between the knee-ankle midpoint line (L1) and long axis of dorsum pedis (L2), ARA (∠ε) was defined as the angle between the long axis of planta pedis (L3) and a line (L5) perpendicular to the horizontal plane (L4); C: varus foot deformity and toeing-in change before surgery; D, the corrected varus deformity and toeing-in change after surgery. ADA = ankle deformity angle, ARA = ankle rotation angle, Uniplane OWHTO = uniplane medial open-wedge high tibial osteotomy.

2.4. Statistical analysis

The intra- and inter-rater intraclass correlation coefficients (ICCs) were used for intra- and inter-observer reliability. ICCs > 0.75 suggested good repeatability and ICCs < 0.40 suggested poor repeatability. We confirmed the sample size using an α-level of 0.05 and a power of 0.8, a power analysis was performed to show the statistical significance of the correlation coefficient (0.418) between the distal tibial rotation and the ∆MPTA, based on the findings of this correlation coefficient in a pilot study involving 8 subjects. Power analysis showed that 36 knees were required to show a statistically significant relationship. This study finally included 37 knees, indicating the power (0.899) was adequate.

Statistical analysis was performed using the SPSS 22.0 software (SPSS, Chicago, IL). All data were presented as mean ± SD. The student’s paired t test was used to assess TRA, FTRA, TT-TG, PTS, HKA, MPTA, ADA, and ARA differences pre- and post-operation. A Pearson correlation analysis was performed to confirm the correlation between the TRA and the change in radiographic parameters before and after HTO. It also identified the variables that independently affected tibial rotation change. Statistically correlated factors were selected and analyzed using multiple linear regression analysis to rule out irrelevant factors. The variables that are statistically correlated with the change in TRA were determined using multiple regression analysis with a stepwise method. The criterion for enrollment in the model was a P value of < .1. Independent variables were excluded from the model if the variable had a P value of > .1. The radiographic data was blinded for 2 measurements by 2 experienced independent observers with a time interval of at least 2 weeks.

3. Results

Baseline characteristics of the patients were shown in Table 1. The mean age was 57.4 ± 6.1 years (46–65). The mean BMI was 25.2 ± 4.1 kg/m² (20.9–34.2). Intra- and inter-rater ICCs of all radiographic parameters showed good agreement in terms of the reliability of radiographic measurements (>0.90).

Table 1.

Baseline characteristics of the patients.

Demographics	Results
Number of knees (patients)	37 (31)
Age (yr)*	57.4 (46–65)
Male/female	12/25
Height (cm)*	162.3 (152–181)
Weight (kg)*	68.6 (47-89)
Body mass index (kg/m2)*	25.2 (20.9–34.2)
Pre-op K-L grade n (%)
Grade 2	15 (11)
Grade 3	18 (16)
Grade4	4 (4)
Deformity (°)*	Varus 7.1 ± 3.4 (2.9–13.6)
Implant	π plate
Complication	hinge fractures (2 cases)
	Venous thromboembolism (2 cases)
	Poor wound healing (1 case)

K-L = Kellgren-Lawrence.

^*Mean ± standard deviation (range).

The measuring outcomes in the knee and ankle joint before and after uniplane OWHTO was shown in Table 2. The mean change in HKA, MPTA was 10.5°±2.9°, 8.8°±2.6°. The mean preoperative and postoperative TRA were 25.1°±6.9° and 22.2°±6.2° respectively (P = .007). Thus, the mean ∆TRA was −3.0° ± 3.4° (IR) with a range of −9.6° to +2.8° after surgery. No significant differences were found in the TT-TG, PTS, and FTRA before and after surgery (P > .05). The postoperative ARA and ADA changed significantly compared with the preoperative value (P < .001). The mean ranges of ARA and ADA were 5.1°±5.8° and 9.9°±7.3° respectively.

Table 2.

The measuring outcomes in the knee and ankle joint before and after uniplane OWHTO.

Measurement parameters	Preoperative	Postoperative	Change (∆)	P value
HKA (°)	−7.0 ± 3.4	3.5 ± 1.4	10.5 ± 2.9	<.001*
MPTA (°)	82.7 ± 2.3	92.9 ± 1.9	10.2 ± 2.6	<.001*
TRA (°)	25.1 ± 6.9	22.2 ± 6.2	−3.0 ± 3.4	.007*
TT-TG (mm)	10.2 ± 4.7	9.0 ± 4.5	−1.2 ± 5.2	.363
PTS (°)	8.8 ± 2.9	8.2 ± 2.9	−0.6 ± 2.0	.103
FTRA (°)	0.2 ± 5.3	1.3 ± 5.3	1.1 ± 5.5	.305
ADA (°)	−4.1 ± 6.2	1.0 ± 2.4	5.1 ± 5.8	.040*
ARA (°)	−1.1 ± 4.2	8.1 ± 6.2	9.2 ± 7.3	.020*

ADA = ankle deformity angle, ARA = ankle rotation angle, FTRA = femorotibial rotation angle, HKA angle = hip-knee-ankle angle, MPTA = medial proximal tibial angle, PTS = posterior tibial slope, TRA = distal tibial rotation angle, TT-TG = tibial tuberosity-trochlear groove distance, Uniplane OWHTO = uniplane medial open-wedge high tibial osteotomy.

^*P < .05.

The ∆HKA (r = 0.726, P = .008) and ∆MPTA (r = 0.860, P = .003) were associated with distal tibial rotation using correlation analysis (Table 3). However, with multiple regression analysis, ∆MPTA was the only predictor of distal tibial rotation (β = 0.667, P = .003, Table 4). The estimated regression equation was described below: ∆TRA = −4.609 + 0.860 × ∆MPTA. The equation indicated that a larger OW was positively correlated with internal rotation of the distal tibia after uniplane MOWHTO.

Table 3.

Correlations between distal tibial rotation and the change in knee-ankle joint before and after uniplane OWHTO.

Dependent variables	Independent variables	Correlation coefficient	P value†
TRA	∆HKA	0.726	.008*
	∆MPTA	0.860	.003*
	∆TT-TG	−0.136	.762
	∆ADA	−0.148	.566
	∆ARA	−0.086	.711

ADA = ankle deformity angle, ARA = ankle rotation angle., HKA angle = hip-knee-ankle angle, MPTA = medial proximal tibial angle, TRA = distal tibial rotation angle, TT-TG = tibial tuberosity-trochlear groove distance, Uniplane OWHTO = uniplane medial open-wedge high tibial osteotomy.

^*P < .05.

^†Pearson correlation test was performed to determine the associated change of radiographic parameters before and after HTO that affect the TRA.

Table 4.

Multiple linear regression analysis of factors affecting the change in tibial rotation after uniplane OWHTO in all included subjects.

Dependent variables	Independent variables	Non-standardized coefficients B	SE	Standardized coefficients β	t value	P value
TRA	Constant	−4.609	2.272	–	−2.028	.061
	∆MPTA	0.860	0.248	0.667	3.465	.003*

The variables that are statistically correlated with the change in TRA were determined using multiple regression analysis with a stepwise method. The criterion for enrollment in the model was a P value of < .1. If the variable has a P value of > .1, the independent variables were excluded from the model.

B = unstandardized coefficients, MPTA = medial proximal tibial angle, SE = standard error, TRA = distal tibial rotation angle, β = standardized coefficients, Uniplane OWHTO = uniplane medial open-wedge high tibial osteotomy.

^*P < .05.

4. Discussion

The main finding in this study is that the distal fragment of the tibia underwent significant internal rotation after uniplane MOWHTO. The osteotomy gap magnitude was positively correlated with rotational misalignment. This study was the first to evaluate the change in axial tibial rotation after uniplane OWHTO.

The changes in sagittal and coronal planes during HTO have been studied extensively.^[6,7,19,20] Considering the three-dimensional structure in the proximal tibia, the change in the axial plane occurred simultaneously during the surgery. However, only a limited amount of research has reported about the rotation change at the distal tibia after HTO.^[8–10] The mean tibial rotation change in previous studies varied widely with a mean range of −3° to +3° in biplane MOWHTO^[11–13] and −5.7° to −1° in CWHTO.^[11,12] In the current study, a mean −3.0° ± 3.4° (IR) with a range from −6.5° to +2.8° was observed after uniplane OWHTO.

Many factors have been studied to understand this wide variance in data. First, the opening gap ratio and greater posterolateral direction of the vertical osteotomy could cause rotational change after biplane OWHTO.^[21] Second, hinge instability and incomplete contact at the ascending plane might be a reason to increase unintentional change in tibial external rotation.^[12,21] In addition, rotational change might be a compensatory mechanism by the lower extremity in adapting to the variety of soft-tissue tension around the knee when opening the osteotomy gap.^[10] The tendon structure around the knee is critical in maintaining the rotational stability of the knee joint.^[11] In the medial knee, the pes anserinus tendon consists of sartorius, gracilis and semitendinosus which act as an internal rotator of the tibia and the medial collateral ligament to control tibia rotation. In the lateral knee, the posterolateral complex (PLC) controls the knee varus and external tibial rotation. In severe OA, degenerative injuries occurred in the PLC because of resistance to increasing knee adduction moment (KAM) of the genua varus. As a result, this indicates a functional decline of the stabilizing knee joint.^[22] Therefore, the different degrees of soft tissue degeneration around the knee might cause various rotational changes after HTO. In addition, due to the reduced KAM when the tibia is everted, the relieved strain of the posterolateral complex can also recover its function to restrict tibial external rotation.^[23]

In the present results, only ∆MPTA was positively correlated with changes in the TRA, indicating that the larger the correction, the greater the free change existing in the distal tibia (Fig. 4). In addition, a hinge fracture occurred in 2 cases with abnormal external rotation (2.0° and 2.8°), indicating an unstable distal tibia. Considering the differences compared to biplane MOWHTO, some anatomical conditions might be considered causative for internal rotation change in uniplane MOWHTO. The first was the absence of the ascending plane existing in biplane MOWHTO. Thus, incomplete contact in the vertical osteotomy gap which increased external rotation would hardly be influenced by uniplane MOWHTO. The second would be consistent with biplane OWHTO where the attenuated PLC strain and enhanced tendon tension of medial soft tissue with increasing OW both contribute to internal rotation. Therefore, the different management of these key structures around the knee joint during surgery might lead to various rotational changes after HTO.^[13]

Figure 4.

Correlation between ∆TRA and ∆MPTA. A significant correlation was found following uniplane OWHTO. ∆TRA, the change in tibial rotation angle. ∆MPTA, the change in medial proximal tibial angle, indicating the opening gap (OW) magnitude. MPTA = medial proximal tibial angle, TRA = distal tibial rotation angle, Uniplane OWHTO = uniplane medial open-wedge high tibial osteotomy.

In recent biomechanical research, Yazdi et al^[24] reported that with 15˚ of external rotation for the distal tibia, the medial compartment contact pressure was decreased by 11% compared to that in the neutral position. However, in order to facilitate external tibial rotation, a tibia shaft and fibulectomy were simultaneously performed. Unlike this, Suero et al^[25] reported that 15˚ of external rotation counteracts the beneficial effect of transferring the pressure to the lateral compartment when performing osteotomy only in the proximal medial tibia. Another more recent biomechanical study by Kim et al^[13] reviewed 42 knees and put forward a viewpoint to avoid excessive distal tibial rotation as much as possible during surgery to reduce the adverse effect on the biomechanical environment around the knee joint. Regrettably, these studies were still lacking in sufficient clinical follow-up evidence for support. Therefore, considering the different opinions in literature, the optimal rotation angle remains to be explored.

Rotational deformation is an important and easily ignored problem in that excessive tibial rotation could increase the pressure on the patellofemoral joint and accelerate cartilage degeneration.^[12,25,26] The abnormal change of tibial tuberosity also has adverse effects on the patellar tracking. Kim et al^[27] conducted a study comparing CWHTO and biplane OWHTO. It was found that the tibial tuberosity centered on the hinge position, moved medially after CWHTO and moved laterally after biplane OWHTO. In both techniques, the osteotomy site was located in the proximal tibial tuberosity, therefore the change in distal tibia rotation might have an adverse effect on the tibial tuberosity. In uniplane OWHTO, the osteotomy site was positioned in the distal third of the tibial tuberosity, with the tibial tuberosity remaining attached to the proximal tibial and the change in distal tibial rotation having a limited effect on the tibial tuberosity position.^[28] Furthermore, the excessive change of PTS and FTRA could provide an adverse influence on the patellofemoral joint, so it could be an influencing factor exerting an unintentional effect on the axial tibial rotation.^[29] In our results, the PTS and FTRA remained unchanged after surgery, which suggested the change of tibia rotation resulted solely from internal rotation of the distal tibia. As a result of internal rotation found in this study and constant position of the tibial tuberosity, the uniplane OWHTO procedure may provide an beneficial effect on the patellofemoral joint. Further research should be conducted to evaluate the correlation between tibial rotation and patellofemoral cartilage degeneration following an arthroscopic procedure.

The toe-out angle ranged from 5 to 10 degrees, and decreasing varus of ankle joint has been observed to be associated with significant reductions in OA progression.^[30,31] Conversely, the abnormal foot posture accompanied by the varus foot and toeing-in change in OA patients was a complex musculoskeletal disorder that was observed in particular for patients suffering from severe OA.^[32–34] In these patients, the abnormal increase in KAM was caused by varus malalignment of lower limb. Then, gradually increasing PLC strain over time was induced by resisting the abnormal increase in KAM for OA patients. This led to enhanced tendon tension in the tibialis anterior muscle accompanied by increasing varus foot deformity and toeing-in change.^[35] In MOWHTO, when opening the OW, the weight bearing line was transferred to the lateral compartment, which induced toeing-out change by relieving the tensional tibialis anterior muscle. The valgus alignment and toeing-out change can decrease the KAM and resist the dynamic mechanical loading that occurs in the medial knee.^[36,37] Consisting with the previous studies, the ADA and ARA changed significantly after uniplane MOWHTO (1.0 ± 2.4, 8.9 ± 6.2, P < .05) (Fig. 3). This contributes to reducing risk - potentially causing OA progression for the medial knee after surgery. Further studies are essential for evaluating the influence of dynamic mechanics of distal tibia rotation on the ankle joint.

There were several limitations to this study. First, the number of patients enrolled was relatively small, so further studies should increase the sample size for more reliable results. Second, the lack of evaluation of the osteotomy direction and hinge position is indeed a limitation in this study. The antero or postero-position of hinge may induce the axial rotational change during the opening of the osteotomy site. However, all operations were performed by one same senior surgeon who standardized the surgical technique parameters, such as hinge position and osteotomy direction. This may minimize the bias related to the surgical technique. Third, the influence of distal tibial rotation on clinical outcomes remains unclear, so we could not predicate that the rotational changes are related to poor clinical outcome. With further medium-long-term follow-up to be implemented to draw a more convincing conclusion. Fourth, we only evaluated uniplane OWHTO. To compare the rotational change more clearly, studies with biplane OWHTO and CWHTO should be performed together.

5. Conclusion

The current study confirms an unintended internal rotation in the distal tibia following uniplane MOWHTO and the rotation in the distal tibia was influenced by the opening width. Surgeron should keep in mind to avoid the osteotomy complication leading to excessive rotation change during surgery.

Acknowledgments

The authors gratefully acknowledge all volunteers who participated in this study.

Author contributions

Conceptualization: Fenglong Sun, Zhanjun Shi.

Formal analysis: Zhanjun Shi.

Investigation: Hengbing Guo, Xin Dong.

Methodology: Ke Li, Hengbing Guo.

Project administration: Ke Li, Fenglong Sun.

Resources: Hongqing Wang.

Software: Hao Zhang, Hongqing Wang.

Supervision: Hao Zhang.

Validation: Ran Yao.

Visualization: Hao Zhang.

Writing – original draft: Ke Li.

Writing – review & editing: Hao Zhang.