Sage Journals: Discover world-class research

Abstract

Purpose:

Medial opening-wedge high tibial osteotomy (OWHTO) induces a lower patellar position, and the subsequent degree of patellar movement may not be predicted preoperatively. The purpose of this study was to clarify the relationship between preoperative and postoperative patellar height based on the correction angle of OWHTO and to create a formula to predict the appearance of patella baja following OWHTO.

Materials and Methods:

Seventy-five knees with varus knee osteoarthritis treated with OWHTO were included in this study. The Caton–Deschamps index was used to evaluate patellar height preoperatively and postoperatively, and the cut-off value for preoperative parameters was determined by a receiver operating characteristic curve to determine the risk ratio for postoperative patella baja.

Results:

The Caton–Deschamps index significantly decreased from 0.93 to 0.77 after OWHTO (p < 0.01). The OWHTO correction angle negatively correlated with the delta Caton–Deschamps index (r = −0.44, p < 0.01), and a 1.7% decrease in the Caton–Deschamps index was shown with a 1° correction angle. Receiver operating characteristic curve analysis revealed that a Caton–Deschamps index of 0.8 was the cutoff for OWHTO; knees with a preoperative Caton–Deschamps index of < 0.8 tended to develop patella baja after OWHTO, with a risk ratio of 9.5 (95% confidence interval [4.3–20.7]).

Conclusions:

OWHTO can induce patella baja, and a 1.7% decrease in the Caton–Deschamps index was shown with a 1°-correction angle. A preoperative Caton–Deschamps index < 0.8 should be considered a risk factor for postoperative patella baja.

Level of Evidence:

Retrospective study, Level IV

Keywords

Caton–Deschamps index opening-wedge high tibial osteotomy patella baja patellar height

Introduction

Opening-wedge high tibial osteotomy (OWHTO) is a successful treatment option for medial compartment knee osteoarthritis (OA). The aim of HTO is to realign the lower limb and shift the load distribution from the medial to the lateral compartment, thereby decreasing OA symptoms in the medial compartment of the knee.^1
–3 HTO changes not only coronal but also sagittal and axial alignment, which affects the femorotibial and patellofemoral joints.^4,5 We had previously reported the occurrence of patellofemoral OA in knees with varus alignment and believed that understanding the critical contributing factors might reduce the likelihood of patellofemoral OA after procedures to correct knee malalignment, such as HTO or total knee arthroplasty.⁶

To evaluate patellar height, different types of measurement have been described, such as the Insall–Salvati index,⁷ Blackburne–Peel index,⁸ modified Miura–Kawamura index,⁹ and Caton–Deschamps index.¹⁰ In particular, the Caton–Deschamps index has been widely used since 1982, originally to assess patellar height after closed wedge HTO and OWHTO.¹¹ Additionally, a multicenter study measuring the patellar heights of more than 300 patients after HTO reported that the Caton–Deschamps index is more reproducible than the Insall–Salvati index.¹²

The progression of patellofemoral OA after HTO has been widely discussed because changes to patellar height caused by HTO might accelerate OA development,^13,14 and HTO has been shown to cause significant and unfavorable changes in patellofemoral mechanics, which are particularly profound after OWHTO.^15,16 All these indicate considering patellofemoral congruity after OWHTO might be essential for the clinical outcomes following HTO. However, the indication of OWHTO based on the preoperative patellar height is still controversial.

The purpose of this study was to measure preoperative and postoperative patellar height and to determine the correlation between the OWHTO correction angle and patellar height based on the Caton–Deschamps index. Subsequently, preoperative indications for OWHTO could be determined to reduce the risk of postoperative patellar baja.

Materials and methods

Seventy-five knees (from 32 men and 43 women) that underwent OWHTO between 2013 and 2016 were retrospectively enrolled in this study. OWHTO was performed in patients with a body mass index (BMI) of less than 35, without diabetes mellitus or with well-controlled disease, and with less than 15° of knee flexion contracture. The mean patient age was 63.1 ± 11.4 years (range, 44–78), and the mean BMI was 24.5 ± 2.9 kg/m² (range 20.8–35.9). Twenty-five patients had Kellgren–Lawrence grade II OA, 38 had grade III OA, and 12 had grade IV OA (Table 1).

Table 1.

Patient characteristics.^a

	OWHTO
Number (male/female)	75 (32/43)
Age (years)	63.1 ± 11.4
Height (m)	1.62 ± 0.09
Weight (kg)	64.0 ± 11.0
BMI (kg/m²)	24.5 ± 2.9
K/L	II: 25, III: 38, IV: 12

BMI: body mass index; K/L: Kellgren–Lawrence; OWHTO: opening-wedge high tibial osteotomy.

^a Data are given as mean values ± standard deviation.

Surgical procedure and assessment

Preoperative planning for HTO first considers the intended postoperative mechanical axis (MA), which passes through the lateral tibial eminence in a coronal view and was determined using digital planning software (TraumaCaD, BRAINLAB, Feldkirchen, Germany) on picture archiving and communication system.^5,17 Biplanar OWHTO was then performed to correct the MA.¹⁸ Arthroscopy was routinely performed prior to HTO to evaluate the degree of cartilage degeneration and synovial hyperplasia. The medial proximal tibia was exposed using a J-shaped incision and the superficial medial collateral ligament and 50% of the pes anserinus attachment was released. Two Kirschner wires (K-wire) were inserted from 35 mm to 40 mm below the knee joint line to the proximal tibiofibular joint as a guide. The osteotomy was performed along the K-wires and then fixed with a locking plate (TomoFix; DePuy Synthes GmbH, Solothurn, Switzerland or Tris Medial HTO Plate System; OLYMPUS, Tokyo, Japan). The gap created by the OWHTO was filled with β-tricalcium phosphate (OLYMPUS). Rehabilitation was initiated on postoperative day 1 with 50% weight-bearing allowed initially and full weight-bearing permitted on day 14.

Preoperative and postoperative knee alignment was compared by measuring the percentage of MA (%MA), which followed a line from center of the femoral head to the center of the ankle joint; the location where this line intersected the tibial plateau was expressed as a percentage of tibial width,¹⁹ the medial proximal tibial angle (MPTA), and posterior tibial slope.⁹ Patellar position was evaluated using the Caton–Deschamps index,^10,20 tibial tuberosity–trochlear groove (TT-TG) distance, and patellar tilt.⁶ The Caton–Deschamps index was determined by measuring the length from the distal end of the patellar joint surface to the anterior tip of the tibial tuberosity, divided by the length of the patellar joint surface, using a lateral view of the knee at a 30° flexion angle. When an osteophyte at the anterior tip of the tibial tuberosity was detected, the Caton–Deschamps index was measured using the original bone shape (Figure 1(a) and (b)). Furthermore, the preoperative, postoperative, and delta Caton–Deschamps indices were analyzed according to the correction angle. The delta Caton–Deschamps index was calculated by dividing the preoperative index by the postoperative index. The pre-post difference was calculated by subtracting the post-OWHTO value to the pre-OWHTO value. Postoperative measurements were performed at the final follow-up, which occurred at an average of 24.8 months (range 18–42 months). The normal range on the Caton–Deschamps index is recognized as 0.6–1.2.²¹ Interobserver and intraobserver reliability for the Caton–Deschamps index were 0.90 and 0.93 in this study, respectively. This study was performed in accordance with a protocol approved by the Institutional Review Board of Osaka Medical College, and all patients provided informed consent (no Rin-217).

Figure 1.

X-Ray knee joint lateral views showing (a) preoperative and (b) postoperative Caton–Deschamps index = A/B.

Statistical analysis

A power analysis was performed for the primary comparison of interest (the correlation between the correction angle and postoperative Caton–Deschamps index). The power analysis was set up as follows: α = 0.05, r = 0.4, and power = 0.8. As a result, 39 knees were the minimum required for the OWHTO sample based on G*power (version 3.1.9.2).²² A paired t-test was performed to compare the preoperative and postoperative radiographic results using JMP Pro (version 11.2.0; SAS Institute Inc., Cary, North Carolina, USA). The preoperative cutoff values were determined by receiver operating characteristic curve. The relative risks for patella baja were analyzed, and the p values of < 0.05 were considered statistically significant.

Results

The preoperative %MA and MPTA were significantly altered from 20.9 ± 11.6% to 60.7 ± 5.8% and from 83.0 ± 2.0° to 92.3 ± 1.6°, respectively (p < 0.01, Table 2). The average correction angle was 9.3° based on the change in MPTA. Preoperative and postoperative posterior tibial slope was not significantly different. In terms of the changes in patellar height and malalignment after HTO, the mean Caton–Deschamps index significantly decreased from 0.93 to 0.77 after OWHTO (p < 0.01, Table 2). On the contrary, TT-TG distance and patellar tilt were not altered postoperatively. To determine the correlation between correction angle and patellar height, the correction angle was compared with the preoperative and postoperative Caton–Deschamps indices and the delta Caton–Deschamps index (Figure 2(a)). The correction angle of the OWHTO did not correlate with the preoperative and postoperative Caton–Deschamps indices, respectively. However, it did correlate with the pre–post Caton–Deschamps index (r = 0.38, p = 0.0008; Figure 2(a)) and delta Caton–Deschamps index (r = −0.44, p < 0.0001; Figure 2(a)). Moreover, it showed a 1.7% decrease in the Caton–Deschamps index with a 1°-correction angle (p < 0.01; Figure 2(b)). In 57 knees (76%), the postoperative Caton–Deschamps index was within the normal range (group N), whereas 18 knees (24%) exhibited patella baja (Caton–Deschamps index < 0.6) after OWHTO (group B; Figure 3(a)). The cutoff values for the preoperative parameters were evaluated, and the preoperative Caton−Deschamps index had the greatest diagnostic value of the parameters measured, with an area under the curve of 0.901. A preoperative Caton−Deschamps index of 0.8 was considered the cutoff value indicating that OWHTO should be performed, as a preoperative Caton−Deschamps index < 0.8 tended to result in patella baja after surgery, with a risk ratio of 9.5 (95% confidence interval 4.3–20.7; Figure 3(b)).

Table 2.

Changes in knee alignment and patellar position with OWHTO.^a

	Preoperative	Postoperative	p value
Knee alignment
%MA	20.9 ± 11.6	60.7 ± 5.8	< 0.01
MPTA (°)	83.0 ± 2.0	92.3 ± 1.6	< 0.01
Posterior tibial slope (°)	8.4 ± 3.5	8.8 ± 3.9	0.54
Patellar position
Caton–Deschamps index	0.93 ± 0.15	0.77 ± 0.16	< 0.01
TT-TG distance (mm)	11.3 ± 2.9	11.6 ± 2.7	0.58
Patellar tilt (°)	8.5 ± 4.7	7.4 ± 4.4	0.24

%MA: percentage of mechanical axis; MPTA: medial proximal tibial angle;

TT-TG: tibial tuberosity–trochlear grove; OWHTO: opening-wedge high tibial osteotomy.

^a Data are given as mean values ± standard deviation.

Figure 2.

(a) Result of linear correlation analysis between the pre–post and delta Caton–Deschamps indices and the correction angle of the OWHTO. (b) The pre–post and delta Caton–Deschamps indices correlated with the degree of the correction angle of the OWHTO. OWHTO: opening-wedge high tibial osteotomy.

Figure 3.

Relative risk of patella baja after OWHTO. (a) Fifty-seven knees had a Caton–Deschamps index within the normal range (group N), whereas 18 knees exhibited patella baja (Caton–Deschamps index < 0.6) after OWHTO (group B). (b) Knees with preoperative Caton–Deschamps index below 0.8 tended to develop patella baja after OWHTO. OWHTO: opening-wedge high tibial osteotomy.

Discussion

The most important findings of this study are that the degree of the OWHTO correction angle of was negatively associated with postoperative patellar height and that the Caton−Deschamps index decreased by 1.7% per degree of 1°-correction angle. A Caton−Deschamps index <0.8 was a high-risk factor for postoperative patella baja.

HTO changes the patellofemoral contact pressure,²³ and cartilage pressure within the patellofemoral joint following OWHTO has been reported to be significantly greater than in an intact knee.¹⁵ Several reports have described changes in postoperative patellar height after HTO procedures,^9,24
–26 and the degree of change correlates with the magnitude of the correction angle.^11,12 In contrast, Lee et al. suggested that mild patellofemoral problems should not be considered a contraindication for the OWHTO procedure.²⁷ In the current study, postoperative patellar height negatively correlated with the correction angle, which was 9.3° on average. Gaasbeek et al. compared patellar height during knee flexion before and after OWHTO and closed wedge HTO and reported that the patella descended after OWHTO and ascended after closed-wedge HTO.¹⁶ Moreover, they reported that a larger correction angle resulted in larger alterations in patellar height after either OWHTO or closed-wedge HTO. Our results were similar to those of previous studies, which showed that greater correction angles induced patella baja after OWHTO.

Patella baja has been described as part of “infrapatellar contracture syndrome” and results in increased patellofemoral contact pressures, pain, and the development of chondromalacia patella.^28,29 However, there are no reports on the indications for OWHTO based on the risk of postoperative patella baja. Here, we clearly showed a 1.7% decrease in the Caton−Deschamps index for each degree of correction angle (p < 0.01). The average correction angle was 9.3° in this study, which was expected to translate into a 16% postoperative decrease in the Caton−Deschamps index. This is consistent with the finding that patients with a preoperative Caton−Deschamps index of < 0.8 tended to develop patella baja after OWHTO. These parameters, based on the Caton−Deschamps index, might be helpful in predicting postoperative patellar height after OWHTO.

Axial change after OWHTO has been discussed and is still controversial.^30
–32 The increased external rotation after OWHTO is likely due to the intact fibula and tibiofibular³⁰; on the other hand, an unintentional increase of internal rotation had occurred at the distal tibia after OWHTO.³² In the current study, axial changes after OWHTO were determined by TT-TG and patellar tilt, as TT-TG might be considered to deteriorate the patellofemoral congruity and subsequently alter patellar tilt. These parameters were not altered in this study, given that the correction angle, which was associated with the degree of axial change, was not significant. Sagittal and axial changes should be considered when a large OWHTO correction is performed.

This study had several limitations. It was a retrospective, consecutive study with a limited number of samples. Also, femoral anteversion, which may affect patellofemoral geometry, was not evaluated. Further research may be needed to determine the association between femoral anteversion and postoperative patellar height after OWHTO.

Conclusion

The Caton−Deschamps index decreased by 1.7% per degree of 1°-correction angle, resulting in an increased risk of patella baja. The risk of postoperative patella baja should be considered when performing OWHTO, especially in patients with a preoperative Caton–Deschamps index < 0.8.

Footnotes

Authors’ contribution

Authors SO, TM, KN, and YO designed the study; SO, TM, KN, YO, NO, and HW analyzed the data; SO, TM, KN, YO, NO, HW, and MN wrote the manuscript; and YO and MN supervised the study.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

References

Coventry

. Osteotomy of the upper portion portion of the tibia. J Bone Joint Surg Am 1965; 47: 984–990.

Schallberger

Jacobi

Wahl

. High tibial valgus osteotomy in unicompartmental medial osteoarthritis of the knee: a retrospective follow-up study over 13-21 years. Knee Surg Sports Traumatol Arthrosc 2011; 19: 122–127.

Amendola

Bonasia

. Results of high tibial osteotomy: review of the literature. Int Orthop 2010; 34: 155–160.

Hinterwimmer

Feucht

Paul

. Analysis of the effects of high tibial osteotomy on tibial rotation. Int Orthop 2016; 40: 1849–1854.

Feucht

Minzlaff

Saier

. Degree of axis correction in valgus high tibial osteotomy: proposal of an individualised approach. Int Orthop 2014; 38(11): 2273–2280. DOI: 10.1007/s00264-014-2442-7.

Otsuki

Nakajima

Okamoto

. Correlation between varus knee malalignment and patellofemoral osteoarthritis. Knee Surg Sports Traumatol Arthrosc 2014; 24: 176–181.

Insall

Salvati

. Patella position in the normal knee joint. Radiology 1971; 101: 101–104.

Blackburne

Peel

. A new method of measuring patellar height. J Bone Joint Surg Br 1977; 59: 241–242.

LaPrade

Oro

Ziegler

. Patellar height and tibial slope after opening-wedge proximal tibial osteotomy: a prospective study. Am J Sports Med 2010; 38: 160–170.

10.

Caton

Deschamps

Chambat

. Patella infera. Apropos of 128 cases. Rev Chir Orthop Reparatrice Appar Mot 1982; 68: 317–325.

11.

Tigani

Ferrari

Trentani

. Patellar height after high tibial osteotomy. Int Orthop 2001; 24: 331–334.

12.

Amzallag

Pujol

Maqdes

. Patellar height modification after high tibial osteotomy by either medial opening-wedge or lateral closing-wedge osteotomies. Knee Surg Sports Traumatol Arthrosc 2013; 21: 255–259.

13.

Gaasbeek

RDA

Sonneveld

van Heerwaarden

. Distal tuberosity osteotomy in open wedge high tibial osteotomy can prevent patella infera: a new technique. Knee 2004; 11: 457–461.

14.

Scuderi

Windsor

Insall

. Observations on patellar height after proximal tibial osteotomy. J Bone Joint Sur Am 1989; 71: 245–248.

15.

Stoffel

Willers

Korshid

. Patellofemoral contact pressure following high tibial osteotomy: a cadaveric study. Knee Surg Sports Traumatol Arthrosc 2007; 15: 1094–1100.

16.

Gaasbeek

Welsing

Barink

. The influence of open and closed high tibial osteotomy on dynamic patellar tracking: a biomechanical study. Knee Surg Sports Traumatol Arthrosc 2007; 15: 978–984.

17.

Kim

Lee

Shin

. Preoperative planning using the picture archiving and communication system technique in high tibial osteotomy. J Orthop Surg (Hong Kong) 2017; 25: 2309499016684701.

18.

Lobenhoffer

Agneskirchner

. Improvements in surgical technique of valgus high tibial osteotomy. Knee Surg Sports Traumatol Arthrosc 2003; 11: 132–138.

19.

Andrews

Noyes

Hewett

. Lower limb alignment and foot angle are related to stance phase knee adduction in normal subjects: a critical analysis of the reliability of gait analysis data. J Orthop Res 1996; 14: 289–295.

20.

Dejour

Walch

Nove-Josserand

. Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatol Arthrosc 1994; 2: 19–26.

21.

Seil

Müller

Georg

. Reliability and interobserver variability in radiological patellar height ratios. Knee Surg Sports Traumatol Arthrosc 2000; 8: 231–236.

22.

Faul

Erdfelder

Buchner

. Statistical power analyses using G*Power 3.1: tests for correlation and regression analyses. Behav Res Methods 2009; 41: 1149–1160.

23.

Bin

Kim

Ahn

. Changes in patellar height after opening wedge and closing wedge high tibial osteotomy: a meta-analysis. Arthroscopy 2016; 32: 2393–2400.

24.

Kesmezacar

Erginer

Ogut

. Evaluation of patellar height and measurement methods after valgus high tibial osteotomy. Knee Surg Sports Traumatol Arthrosc 2005; 13: 539–544.

25.

Portner

. High tibial valgus osteotomy: closing, opening or combined? Patellar height as a determining factor. Clin Orthop Relat Res 2014; 472: 3432–3440.

26.

Gaasbeek

RDA

Nicolaas

Rijnberg

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

27.

Lee

. Changes in patellofemoral alignment do not cause clinical impact after open-wedge high tibial osteotomy. Knee Surg Sports Traumatol Arthrosc 2014; 24: 1–5.

28.

Lancourt

Cristini

. Patella alta and patella infera. Their etiological role in patellar dislocation, chondromalacia, and apophysitis of the tibial tubercle. J Bone Joint Surg Am 1975; 57: 1112–1115.

29.

Meyer

Brown

Pedersen

. Retropatellar contact stress in simulated patella infera. Am J Knee Surg 1997; 10: 129–138.

30.

Baumgarten

Meyers

Fealy

. The coronal plane high tibial osteotomy. Part II: a comparison of axial rotation with the opening wedge high tibial osteotomy. HSS J 2007; 3: 155–158.

31.

Jacobi

Villa

Reischl

. Factors influencing posterior tibial slope and tibial rotation in opening wedge high tibial osteotomy. Knee Surg Sports Traumatol Arthrosc 2014; 23: 2762–2768.

32.

Jang

Lee

Park

. Unintended rotational changes of the distal tibia after biplane medial open-wedge high tibial osteotomy. J Arthroplasty 2016; 31: 59–63.

Risk of patella baja after opening-wedge high tibial osteotomy

Abstract

Purpose:

Materials and Methods:

Results:

Conclusions:

Level of Evidence:

Keywords

Introduction

Materials and methods

Surgical procedure and assessment

Statistical analysis

Results

Discussion

Conclusion

Footnotes

Authors’ contribution

Declaration of conflicting interests

Funding

References