Comparison of Patellofemoral Degeneration After Three Types of High Tibial Osteotomy: Retrotuberosity Biplane Open-Wedge, Supratuberosity Biplane Open-Wedge, and Closed-Wedge Techniques

Abstract

Background:

Retrotuberosity biplane open-wedge high tibial osteotomy (RTOWHTO) may reduce negative patellofemoral joint outcomes. However, no studies have compared patellofemoral cartilage degeneration between RTOWHTO and supratuberosity biplane open-wedge high tibial osteotomy (STOWHTO) using arthroscopic assessment nor compared patellofemoral cartilage degeneration or radiographic patellofemoral-specific parameters between RTOWHTO and closed-wedge high tibial osteotomy (CWHTO).

Purpose:

To compare the arthroscopically assessed femoral trochlear cartilage degeneration and radiographic patellofemoral-specific parameters after RTOWHTO, STOWHTO, and CWHTO.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

A total of 58 RTOWHTOs, 59 STOWHTOs, and 88 CWHTOs were examined using first-look arthroscopy between 2013 and 2022. The demographics did not differ significantly between the groups. Hardware removal and second-look arthroscopy were performed, on average, 29.7, 26.9, and 26.7 months after the RTOWHTOs, STOWHTOs, and CWHTOs, respectively (P = .30). Degeneration of the femoral trochlear cartilage was arthroscopically evaluated using the International Cartilage Regeneration & Joint Preservation Society grading system. Patellar translation and height were evaluated radiographically, and patellar height was assessed using the modified Blackburne-Peel ratio.

Results:

The prevalence rates of femoral trochlear cartilage degeneration were 17.2% (10/58), 39% (23/59), and 19.3% (17/88) in the RTOWHTO, STOWHTO, and CWHTO groups, respectively (P = .008). The prevalence was significantly higher in STOWHTOs than in both RTOWHTOs and CWHTOs (both P = .01), but not significantly different between RTOWHTOs and CWHTOs (P = .83). The increase in lateral patellar translation was significantly greater in the STOWHTOs (1.1 ± 1.5 mm) than in both the RTOWHTOs (–0.1 ± 2.0 mm) and the CWHTOs (0.5 ± 1.2 mm) (P = .001 and .04, respectively). There was no significant difference between the RTOWHTOs and CWHTOs with respect to the increases in lateral translation (P = .10). The lowering in patellar height was significantly greater after the STOWHTOs (–0.2 ± 0.1) than after both the RTOWHTOs (0.0 ± 0.1) and the CWHTOs (–0.1 ± 0.2) (P < .001 and .002, respectively). The lowering was significantly smaller in the RTOWHTOs than in the CWHTOs (P = .02).

Conclusion:

RTOWHTO may provide favorable patellofemoral joint outcomes, with a lower prevalence of trochlear cartilage degeneration and less lateral patellar translation than STOWHTO, as well as less patellar height lowering than both STOWHTO and CWHTO.

Open-wedge high tibial osteotomy (OWHTO) is a well-established procedure for the treatment of medial compartment osteoarthritis with varus alignment, with the advantage of facilitating precise intraoperative correction. Among the available methods, the supratuberosity biplane approach is commonly used, incorporating an additional ascending osteotomy to improve rotational stability and promote gap healing (Figure 1).^21,35 However, since osteotomy is performed proximal to the tibial tuberosity, and gap opening causes lateralization and distalization of the tuberosity, there is a potential for increase in the Q angle, patella infera, and adverse effects on the patellofemoral joint.^16,30

Figure 1.

Study flowchart. CWHTO, closed-wedge high tibial osteotomy; HTO, high tibial osteotomy; ICRS, International Cartilage Regeneration & Joint Preservation Society; RTOWHTO, retrotuberosity biplane open-wedge high tibial osteotomy; STOWHTO, supratuberosity biplane open-wedge high tibial osteotomy.

Closed-wedge high tibial osteotomy (CWHTO) is considered a treatment option to avoid patellofemoral problems due to proximal migration of the tibial tuberosity following wedge closure. Many studies have reported better patellofemoral-specific outcomes after CWHTO than after supratuberosity biplane OWHTO (STOWHTO).^12,30,31 However, CWHTO is technically demanding, particularly with respect to intraoperative adjustment for precise correction.

In retrotuberosity biplane OWHTO (RTOWHTO), additional cutting is performed obliquely and distally to the tibial tuberosity. ⁶ This technique can facilitate intraoperative correction adjustment and help avoid negative effects to the patellofemoral joint, as the tuberosity remains in the proximal fragment, thereby minimizing lateralization of the tibial tuberosity and patellar lowering.^5,6 Previous studies have reported better patellofemoral-specific radiographic parameters after RTOWTHO than after STOWHTO.^5,7,15,16,22

To date, no studies have compared patellofemoral cartilage degeneration between RTOWHTO and STOWHTO using arthroscopic assessments. Additionally, no study has compared patellofemoral cartilage degeneration or radiographic patellofemoral-specific parameters between RTOWHTO and CWHTO.

The purpose of our study was to compare arthroscopically assessed femoral trochlear cartilage degeneration and radiographic patellofemoral-specific parameters following RTOWHTO, STOWHTO, and CWHTO. It was hypothesized that the patellofemoral-specific outcomes of RTOWHTO would be superior to those of STOWHTO and comparable with those of CWHTO.

Methods

Patients

Using our hospital database, we retrospectively searched for patients who underwent index RTOWHTO, STOWHTO, and CWHTO with first-look arthroscopy and hardware removal with second-look arthroscopy. The inclusion criteria were as follows: (1) patients who underwent appropriate arthroscopic observation of the femoral trochlear cartilage during first- and second-look arthroscopy (this study focused solely on the arthroscopic evaluation of the femoral trochlear cartilage owing to the limited reliability of patellar cartilage assessment), (2) patients whose appropriate arthroscopic images of the trochlear cartilage captured during first- and second-look arthroscopy were saved in our database, and (3) patients with available appropriate pre- and postoperative radiographs. The exclusion criteria were patients (1) with a history of trauma, infection, or previous surgery on the affected knee; (2) with instability of the affected knee owing to any ligament problem; (3) who underwent a concurrent cartilage procedure on the femoral trochlea during high tibial osteotomy (HTO); (4) with International Cartilage Regeneration & Joint Preservation Society (ICRS) grade 4 lesion in the trochlear cartilage on first-look arthroscopy, making it difficult to evaluate whether the cartilage lesion had progressed; and (5) with postoperative complications potentially influencing patellofemoral-specific outcomes (eg, coronal or sagittal correction loss, tibial tuberosity fracture, delayed union or nonunion of the ascending or descending osteotomy site, or arthrofibrosis).

According to these criteria, 58 RTOWHTOs, 59 STOWHTOs, and 88 CWHTOs performed between 2013 and 2022 were included (Figure 1). Since 2019, RTOWHTO has been adopted at our institution instead of STOWHTO primarily because of concerns regarding patellofemoral joint degeneration. The surgical indications for all HTO procedures were the same: (1) symptomatic medial compartment osteoarthritis (Kellgren-Lawrence grades 2-3); (2) varus deformity from 5° to 15°; (3) flexion contracture of <15° and flexion angle >90°; and (4) absence of symptomatic lateral compartmental and patellofemoral arthritis, active infection, inflammatory arthritis, and lateral tibial subluxation of >1 cm.

There were no significant differences in demographics among the RTOWHTO, STOWHTO, and CWHTO groups preoperatively (Table 1). Informed consent was obtained from all patients for operative procedures and prior to review, and this study was approved by the institutional review board of our hospital.

Table 1.

Demographic Data ^a

	RTOWHO	STOWHTO	CWHTO	P
Knees, n	58	59	88
Age, y	58.3 ± 5.0	56.5 ± 9.3	57.7 ± 5.6	.34
Female/male, n	43/15	44/15	77/11	.07
Body mass index, kg/m2	25.9 ± 2.9	25.5 ± 2.9	25.7 ± 3.0	.73
Period from index HTO to hardware removal, mo	29.7 ± 9.1	26.9 ± 11.2	26.7 ± 12.3	.30

^aData are presented as mean ± SD unless otherwise indicated. CWHTOS, closed-wedge high tibial osteotomy; HTO, high tibial osteotomy; RTOWHTO, retrotuberosity biplane open-wedge high tibial osteotomy; STOWHTO, supratuberosity biplane open-wedge high tibial osteotomy.

Surgical Techniques

Three orthopaedic surgeons performed all HTO procedures. Two surgeons (K.H.Y., C.H.P.) performed RTOWHTO and STOWHTO, while the other surgeon (S.J.S.) performed CWHTO. All surgeons adhered to the same indications and surgical principles. The Dugdale method was used for preoperative planning on anteroposterior long-leg weightbearing radiographs. ²⁴ The postoperative hip-knee-ankle (HKA) angle was targeted at 2° of valgus, with the weightbearing line from the hip center to the ankle center aimed to pass through 55% to 60% of the tibial plateau width.^14,18,29 If required, arthroscopic procedures such as cartilage debridement, microfracture, partial meniscectomy, or meniscal repair were performed in the medial compartment prior to osteotomy.

In all OWHTOs, a vertical incision was made on the anteromedial proximal tibia, followed by release of the pes anserinus and superficial medial collateral ligament to expose the tibial surface. Two guide pins for the main osteotomy were inserted obliquely toward the tibiofibular joint. ²⁵ RTOWHTO involved biplanar osteotomy with a main axial cut and descending coronal cut distal to the tibial tuberosity, including the tuberosity in the proximal fragment (Figure 2). ³³ In contrast, STOWHTO used an ascending coronal cut proximal to the tuberosity, leaving it in the distal fragment (Figure 2). ³⁰ The main osteotomy site was opened for target alignment using a spreader and fixed with a medial locking plate (Nowmedipia) and a metal wedge spacer. In RTOWHTO, an additional anteromedial staple was applied to the descending cut to prevent a postoperative posterior tibial slope (PTS) increase. ³³

Figure 2.

Three types of high tibial osteotomy. The red dashed lines indicate the osteotomy planes. CWHTOS, closed-wedge high tibial osteotomy; RTOWHTO, retrotuberosity biplane open-wedge high tibial osteotomy; STOWHTO, supratuberosity biplane open-wedge high tibial osteotomy.

In CWHTO, a transverse incision was made on the anterolateral side of the proximal tibia, followed by dissection of the tibialis anterior muscle. Partial resection of the fibular head was performed to prevent fibular tethering during wedge closure. Under fluoroscopic guidance, one pin was inserted into the proximal level of the wedge, 1.5 cm below the joint line, and another into the distal level to determine alignment correction; the wedge size was determined based on preoperative radiographic planning. Uniplanar osteotomies were then performed along the guide pins, with the osteotomy levels proximal to the tibial tuberosity and their anterior ends near the distal part of the patellar tendon (Figure 2). After wedge removal and careful closure of the osteotomy site, fixation was achieved using a miniplate staple (U&I).

A standardized rehabilitation protocol was applied to all patients: isometric exercises were initiated on the day of surgery, straight-leg raising exercises commenced at the second to third days postoperatively, tolerable weightbearing was allowed at the third to fourth days after surgery, and full weightbearing without crutches was permitted between 6 and 12 weeks postoperatively depending on the patient's clinical condition.

Having radiographically confirmed bone union at the site of osteotomy, removal of hardware and second-look arthroscopy were recommended at 2 years postoperatively, regardless of patients’ clinical symptoms. Second-look arthroscopy was routinely recommended, as performing the procedure under anesthesia during the removal of hardware is considered advantageous with respect to identifying further knee joint lesions and facilitating supplementary intervention when necessary. The interval from the index HTO to hardware removal was not significantly different among the 3 groups (Table 1).

Arthroscopic Evaluation

The femoral trochlear cartilage status was evaluated using the ICRS grading system during the first- and second-look arthroscopies. A primary evaluation was conducted by the surgeons intraoperatively, and the determined grades were recorded in our database. Additionally, another reviewer (CHP) with >5 years of arthroscopic surgical experience retrospectively evaluated the cartilage status using arthroscopic images saved in the database. Interobserver agreement between the surgeons and the retrospective reviewer in determining the ICRS grading was checked using Cohen kappa coefficient. All kappa coefficients in the RTOWHTOs, STOWHTOs, and CWHTOs were >0.8. Thus, the ICRS grades determined by the surgeons were used in this study.

The second-look arthroscopic grading results were compared with those of the first-look arthroscopic grading. The trochlear cartilage degeneration was determined when progression of ≥1 ICRS grade was observed. Advanced degeneration of the cartilage was defined as progression of ≥2 ICRS grades.

Clinical Evaluation

The Western Ontario and McMaster Universities Arthritis Index (WOMAC), range of motion (ROM), and Anterior Knee Pain Scale (AKPS; Kujala score) were evaluated before the index HTO and immediately before hardware removal. ⁸ The ROM was measured using a long-armed goniometer.

Radiographic Evaluation

Radiographic parameters were assessed before HTO and immediately before hardware removal. The long-leg and lateral radiographs were obtained during full knee extension under weightbearing conditions. The Merchant view was obtained with patient placed on a table in the supine position with the knee flexed at an angle of 45°.

The HKA and medial proximal tibial angle (MPTA) were measured on the long-leg radiograph. ¹¹ The PTS was assessed on the lateral knee radiographs; the change in PTS was defined as the postoperative minus preoperative PTS, with a larger value indicating an increase in PTS. ³⁰

The patellar tilt and translation were measured on Merchant views. The patellar tilt angle was defined as the angle between the equatorial line of the patella and the line connecting the anterior margin of the femoral condyles, with a positive value indicating lateral tilting of the patella. ² The patellar translation was defined as the position of the patellar ridge relative to the trochlear sulcus of the femur, a positive value of which was taken to indicate a lateral translation of the patella. ² Changes in patellar tilt and translation were defined as postoperative minus preoperative values, with positive values indicating an increase in lateral patellar tilt and lateral translation.

Patellar height was assessed using the modified Blackburne-Peel ratio (mBPR) on the lateral knee radiograph.^28,30 The mBPR was defined as the perpendicular distance from the lower margin of the patellar articular surface to the tibial plateau line divided by the length of the patellar articular surface (normal range, 0.5-0.9). ³⁰ The change in mBPR was defined as the postoperative minus preoperative mBPRs, with a negative value indicating a lowering in patellar height.

The quality of the radiographic evaluations was enhanced by adopting a standardized radiographic procedure that enabled the control of knee positioning, the direction of X-ray beams, and the distances between the radiographic source, patient, and cassette.^26,27 The images were analyzed using a picture archiving and communication system (Infinitt) that could detect minimal differences of 0.1° and 0.1 mm. Two independent investigators (M.S.K., C.H.P.) measured all radiographic parameters to reduce observational bias. The interobserver reliability of the measurements was assessed using intraclass correlation coefficients, which were all >0.8 in value, and the mean values were used.

Statistical Analysis

The arthroscopic cartilage status presented by the ICRS grade was compared between the first- and second-look arthroscopies using the Wilcoxon signed-rank test. The prevalence of trochlear cartilage degeneration and advanced degeneration were compared among the groups using the chi-square test or Fisher exact test. Data normality of clinical and radiographic results was confirmed using the Kolmogorov-Smirnov test. The pre- and postoperative clinical outcomes were compared using the paired t test. The clinical and radiographic results of the RTOWHTOs, STOWHTOs, and CWHTOs were compared using the analysis of variance, and Tukey test or Dunnett T3 test were used for the post hoc analysis. The AKPS between the groups with and without trochlear cartilage degeneration were compared using the Mann-Whitney U test. Statistical analyses were performed using SPSS Version 25.0 (SPSS Inc), with P values <.05 considered statistically significant.

Post hoc power analysis using significance levels set to an alpha of .05 was performed to determine whether the sample had sufficient power to detect significant differences. A power >80% was considered adequate, and all variables with significant differences met this criterion, indicating that the study was adequately powered.

Results

Arthroscopically, the second-look ICRS grading of the femoral trochlear cartilage significantly changed in the RTOWHTO, STOWHTO, and CWHTO groups compared with the first-look grading (P = .001, <.001, and .001, respectively) (Table 2). The prevalence of trochlear cartilage degeneration was 17.2% (10/58) in the RTOWHTOs, 39% (n = 23/59) in the STOWHTOs, and 19.3% (17/88) in the CWHTOs (P = .008) (Figure 3). The prevalence of degeneration was significantly higher in the STOWHTOs than in the RTOWHTOs and CWHTOs (both P = .01). There was no significant difference in the prevalence between the RTOWHTOs and CWHTOs (P = .83). The prevalences of advanced trochlear degeneration in RTOWHTOs, STOWHTOs, and CWHTOs were 3.4% (2/58), 6.8% (4/59), and 5.7% (5/88), respectively (P = .72).

Table 2.

Change in the International Cartilage Regeneration & Joint Preservation Society Grade (0/1/2/3/4) of the Femoral Trochlear Cartilage ^a

	Preoperative	Postoperative	P
RTOWHTO, n = 58	6/16/14/22/0	4/16/10/24/4	.001
STOWHTO, n = 59	7/19/21/12/0	6/10/18/23/2	<.001
CWHTO, n = 88	7/37/20/24/0	7/25/24/30/2	.001

^aCWHTOS, closed-wedge high tibial osteotomy; RTOWHTO, retrotuberosity biplane open-wedge high tibial osteotomy; STOWHTO, supratuberosity biplane open-wedge high tibial osteotomy.

Figure 3.

Proportions of femoral trochlear cartilage degeneration after high tibial osteotomy. CWHTO, closed-wedge high tibial osteotomy; N.S., nonsignificant; RTOWHTO, retrotuberosity biplane open-wedge high tibial osteotomy; STOWHTO, supratuberosity biplane open-wedge high tibial osteotomy.

Clinically, the WOMAC, ROM, and AKPS improved postoperatively in the RTOWHTOs, STOWHTOs, and CWHTOs (P < .001, respectively). There were no significant differences in the pre- and postoperative clinical results among the groups; although the postoperative AKPS tended to be lower in the STOWHTOs than in the other groups, there was no significant difference (Table 3).

Table 3.

Clinical Results ^a

		RTOWHTO	STOWHTO	CWHTO	P
WOMAC	Preop	59.7 ± 5.8	59.9 ± 4.4	58.2 ± 6.1	.11
	Postop	14.9 ± 4.1	15.8 ± 4.6	14.9 ± 3.2	.08
Anterior Knee Pain Scale	Preop	66.9 ± 8.2	66.8 ± 9.8	67.4 ± 6.4	.89
	Postop	79.3 ± 8.8	76.5 ± 9.1	78.2 ± 7.2	.19
ROM, deg	Preop	132.5 ± 13.3	133.1 ± 14.3	134.6 ± 10.2	.56
	Postop	138.1 ± 6.6	137.9 ± 7.9	139.9 ± 5.2	.11

^aData are presented as mean ± SD. CWHTOS, closed- wedge high tibial osteotomy; Postop, postoperative; Preop, preoperative; ROM, range of motion; RTOWHTO, retrotuberosity open-wedge biplane high tibial osteotomy; STOWHTO, supratuberosity biplane open-wedge high tibial osteotomy; WOMAC, Western Ontario and McMaster Universities Arthritis Index.

The AKPS did not differ preoperatively between the groups with and without trochlear degeneration across the RTOWHTOs, STOWHTOs, and CWHTOs (Table 4). Although the scale tended to be lower postoperatively in the degenerative group for all HTO types, no significant differences were observed.

Table 4.

Comparison of Anterior Knee Pain Scale Between the Groups With and Without Trochlear Degeneration ^a

	RTOWHO			STOWHTO			CWHHTO
	Degen	Nondegen	P	Degen	Nondegen	P	Degen	Nondegen	P
Preoperative	70 (6.75)	69 (10.25)	.35	69 (10.0)	68.5 (10.0)	.65	69 (8.0)	69 (8.0)	.67
Postoperative	77.5 (8.0)	81.5 (9.5)	.18	75 (6.0)	80 (5.5)	.06	75 (11.0)	80 (7.0)	.07

^aData are presented as median (IQR). CWHTOS, closed-wedge high tibial osteotomy; Degen, with degeneration; Nondegen, without degeneration; RTOWHTO, retrotuberosity biplane open-wedge high tibial osteotomy; STOWHTO, supratuberosity biplane open-wedge high tibial osteotomy.

Radiographically, there were no significant differences in the preoperative and postoperative HKA, MPTA, and PTS among the 3 groups; changes in these values were also similar (Table 5). Although there was no significant change in patellar tilt among the groups, the increase in lateral patellar translation was significantly greater in the STOWHTOs than in both the RTOWHTOs and CWHTOs (Table 5). There was no significant difference in the increase in lateral translation between the RTOWHTOs and CWHTOs (Table 5). The change in mBPR (lowering of the patellar height) was significantly greater after the STOWHTOs than after both the RTOWHTOs and the CWHTOs (Table 5). The lowering was significantly smaller in the RTOWHTOs than in the CWHTOs.

Table 5.

Radiographic Results ^a

		RTOWHTO	STOWHTO	CWHTO	P
Mechanical axis, deg	Preop	Varus, 7.8 ± 2.9	Varus, 7.6 ± 4.7	Varus, 8.1 ± 3.0	.77
	Postop	Valgus, 1.7 ± 2.6	Valgus, 2.3 ± 4.1	Varus, 1.2 ± 2.7	.14
	Change	9.5 ± 4.1	9.9 ± 3.4	9.3 ± 3.1	.56
Medial proximal tibial angle, deg	Preop	84.8 ± 2.0	84.7 ± 2.3	84.2 ± 2.5	.19
	Postop	92.0 ± 2.6	92.9 ± 2.4	92.2 ± 2.5	.12
	Change	7.2 ± 3.0	8.2 ± 2.6	8.0 ± 2.4	.07
Posterior tibial slope, deg	Preop	11.3 ± 3.4	11.8 ± 2.5	11.5 ± 3.1	.64
	Postop	11.0 ± 3.3	12.2 ± 5.0	10.8 ± 3.3	.07
	Change	–0.3 ± 2.5	0.4 ± 5.0	–0.7 ± 3.3	.17
Change in patellar tilt, deg		–1.6 ± 2.9	–2.2 ± 3.6	–1.5 ± 3.8	.46
Change in patellar translation, mm		–0.1 ± 2.0	1.1 ± 1.5	0.5 ± 1.2	.001
Modified Blackburn-Peel ratio	Preop	0.8 ± 0.2	0.8 ± 0.1	0.8 ± 0.2	.49
	Postop	0.8 ± 0.2	0.6 ± 0.1	0.7 ± 0.2	<.001
	Change	0.0 ± 0.1	–0.2 ± 0.1	–0.1 ± 0.2	<.001

^aData are presented as mean ± SD. Post hoc analysis for the postoperative modified Blackburn-Peel ratio: RTOWHTO vs STOWHTO, P < .001; STOWHTO vs CWHTO, P < .001; RTOWHTO vs CWHTO, P = .13. Post hoc analysis for the changes in the modified Blackburn-Peel ratio: RTOWHTO vs STOWHTO, P < .001; STOWHTO vs CWHTO, P = .002; RTOWHTO vs CWHTO, P = .02. Post hoc analysis for the changes in patellar translation: RTOWHTO vs STOWHTO, P = .001; STOWHTO vs CWHTO, P = .04; RTOWHTO vs CWHTO, P = .10. CWHTOS, closed-wedge high tibial osteotomy; Postop, postoperative; Preop, preoperative; RTOWHTO, retrotuberosity biplane open-wedge high tibial osteotomy; STOWHTO, supratuberosity biplane open-wedge high tibial osteotomy.

Discussion

The most important finding of the present study was that the trochlear cartilage degeneration, assessed arthroscopically, was significantly less severe following RTOWHTO compared with STOWHTO and was comparable with that observed after CWHTO. The increase in lateral patellar translation showed a trend similar to that of trochlear cartilage degeneration. The lowering in patellar height was significantly smaller after RTOWHTO than after both STOWHTO and CWHTO.

The negative effect on the patellofemoral joint has been an established concern associated with STOWHTO, whereas CWHTO is relatively less implicated in this regard. A previous cadaveric study reported that STOWHTO increased the patellofemoral contact pressure relative to that observed in an intact knee at 30°, 60°, and 90° of knee flexion, whereas CWHTO did not significantly influence the contact pressure at any flexion angle. ³¹ Ishimatsu et al ¹² found that STOWHTO led to worse outcomes in radiographic patellofemoral congruity than hybrid CWHTO despite less severe preoperative patellofemoral osteoarthritis in the STOWHTO group. A recent arthroscopic study demonstrated that the incidence of patellofemoral cartilage degeneration was 44% after STOWHTO and 29.6% after CWHTO, although this difference was not statistically significant because of the small sample size. ³⁰ However, CWHTO is technically demanding, particularly for intraoperative correction adjustments.

RTOWHTO retains the advantage of convenient intraoperative correction adjustment inherent to OWHTO, while minimizing lateralization of the tuberosity and patellar lowering, thereby potentially leading to more favorable outcomes in the patellofemoral joint. Numerous previous studies have demonstrated the advantages of RTOWHTO for the patellofemoral joint. Cho et al ⁵ reported that RTOWHTO showed more favorable outcomes than STOWHTO with respect to the tibial tuberosity position, as reflected by tibial tubercle–trochlear groove (TT-TG) distance, TT-TG angle, and femoral shaft–patellar tendon angle. Esenkaya and Unay ⁶ reported that radiographic patellar height, measured using the Insall-Salvati ratio, original BPR, and Caton-Deschamps index (CDI), did not change significantly after RTOWTHO. A recent meta-analysis demonstrated that RTOWHTO results in less change in patellar height, as measured by both the BPR and the CDI, compared with STOWHTO. ²²

The advantages of RTOWHTO for the patellofemoral joint were clearly supported by our arthroscopic assessment of the femoral trochlear cartilage degeneration. The incidence of trochlear degeneration after RTOWHTO was significantly lower than that after STOWHTO and was comparable with that after CWHTO, although the prevalence of advanced trochlear degeneration was not significantly different among the groups.

Our findings regarding patellar translation similarly provide evidence for the advantages of RTOWHTO. It is well-established that an increase in lateral patellar translation is associated with patellofemoral degeneration. ³² In our study, the RTOWHTO group demonstrated a significantly smaller increase in lateral patellar translation than the STOWHTO group, while showing a comparable degree of translation to the CWHTO group. This may be attributable to the minimal lateralization of the tibial tuberosity associated with RTOWHTO, which likely mitigates increases in the Q angle. ⁵ A previous computer simulation study also reported less lateral patellar translation after RTOWHTO than after STOWHTO. ¹³

The most notable advantage of RTOWHTO was the preservation of patellar height. The radiographic analysis showed that the lowering in patellar height was smaller after RTOWHTO compared not only with STOWHTO but also with CWHTO. This may be because, in RTOWHTO, the osteotomy plane is created distal to the patellar tendon, minimizing postoperative changes in the tendon and surrounding tissues. Keyhani et al ¹⁵ reported that the patellar tendon length did not change significantly after RTOWHTO. In contrast, in our CWHTO group, the osteotomy plane was created at the distal level of the patellar tendon, potentially leading to adhesion, fibrosis, and shortening of the tendon.^3,9 Gokay et al ⁹ demonstrated significant shortening of the patellar tendon along with evident inflammation and fibrotic changes at the distal part of the patellar tendon following CWHTO performed using a technique similar to ours.

Previous studies have suggested that a change in the BPR >0.1 to 0.15 represents a significant alteration in patellar height.^19,23 However, whether such changes are truly clinically meaningful has not been clearly established. In the present study, compared with the RTOWHTOs, which showed no change in mean patellar height, the STOWHTOs demonstrated a 0.2 decrease in the mBPR and was associated with a significantly higher prevalence of trochlear cartilage degeneration. In contrast, CWHTO, which showed a 0.1 decrease in mBPR, did not demonstrate a significant increase in the prevalence of trochlear degeneration compared with RTOWHTO. Although our findings cannot establish the minimally clinically important difference for changes in patellar height, they support the notion that the previously proposed thresholds for “significant” changes in patellar height may indeed be clinically relevant.

The effect of patellofemoral degeneration on postoperative clinical outcomes following HTO remains controversial. A previous study reported an association between postoperative anterior knee pain and ICRS grade of the patellofemoral joint assessed during second-look arthroscopy. ¹⁷ However, a recent study from the same group demonstrated that although arthritic progression of the patellofemoral joint was observed over time following OWHTO, these changes did not affect clinical outcomes. ³⁴ In our study, the patients with trochlear degeneration tended to have lower AKPS scores than those without degeneration. Additionally, the STOWHTO group, which showed a higher incidence of trochlear degeneration, demonstrated a trend toward lower scales. Although these differences were not statistically significant in our sample, they may reach significance in larger sample sizes.

Based on our results, RTOWHTO may provide relatively more favorable outcomes with respect to the patellofemoral joint than other comparable techniques. However, RTOWHTO has several disadvantages compared with other types of HTO. In this technique, traction from the patellar tendon may induce posterior tilting of the proximal fragment, thereby increasing the risk of posterior tibial slope elevation after surgery; an additional operative procedure should be performed to mitigate this risk.^5,16,33 Moreover, RTOWHTO may be associated with complications such as tibial tuberosity protrusion, as well as delayed union at the secondary descending osteotomy plane.^16,22 Therefore, it is imperative to carefully assess the advantages and disadvantages of each type of HTO procedure and to select the approach that is most suitable for the patient and technically feasible for the surgeon.

Limitations

The present study has some limitations. First, this was a retrospective study. Patients who declined second-look arthroscopy were excluded, which could have introduced selection bias. In addition, there was no randomization in the group assignment. A prospective randomized study with a more elaborate design would have provided more robust data. Second, the sample size was relatively small, although the power of our study was appropriate. If the sample size had been larger, the interpretation of the patellofemoral-related clinical results may have changed. Third, this study presented short-term results based on the time of hardware removal. The short-term follow-up period might have contributed to the overall favorable clinical outcomes at the final follow-up, making it difficult to detect significant differences in outcomes. Fourth, the ICRS grading system was used to evaluate the patellofemoral cartilage, which is based solely on cartilage lesion depth and does not account for lesion size. A grading system based on the criteria for lesion size was not used as the surface area and thus could not be evaluated in the retrospective review of medical records and saved arthroscopic images. However, the size of cartilage lesions tends to increase as the ICRS grade of the lesion progresses in the patellofemoral joint.^1,10 Accordingly, it is reasonable to evaluate the overall degeneration of the patellofemoral cartilage based on the ICRS grade. Fifth, we assessed only the degeneration of the trochlear cartilage in the patellofemoral joint since the patellar cartilage was frequently not accurately evaluated in our second-look arthroscopy. However, given that degeneration of the patellofemoral joint predominantly occurs in the femoral trochlea rather than in the patella, the results of this study are meaningful. ²⁹ Sixth, 3 surgeons performed the procedures, although all the surgeons used the same indications and surgical principles for HTO. Additionally, the RTOWHTOs were performed later than the STOWHTOs. These limitations could have led to performance bias. Seventh, additional patellofemoral-specific parameters, such as the TT-TG distance, could not be evaluated because computed tomography was not routinely performed for the patients in the study cohort. Finally, several factors should be taken into consideration when extrapolating the results of this study. Specifically, most patients were female because symptomatic medial compartment osteoarthritis of Kellgren-Lawrence grades 2 or 3 is more prevalent among women in Asian populations.^4,20

Conclusion

RTOWHTO may provide favorable patellofemoral joint outcomes, with a lower prevalence of trochlear cartilage degeneration and less lateral patellar translation than STOWHTO, as well as less patellar height lowering than both STOWHTO and CWHTO.