Abstract
Background:
Trochleoplasty aims to correct trochlear dysplasia, an osseous cause of patellar instability. The procedure involves the use of a high-speed bur directly under femoral articular cartilage, which may place chondrocytes at risk of thermal necrosis.
Purpose/Hypothesis:
The purpose of this study was to investigate the effect of irrigation and offset used during a trochleoplasty procedure on trochlear chondrocyte viability. It was hypothesized that thermal necrosis would be induced by burring and would be mitigated with saline irrigation.
Study Design:
Controlled laboratory study.
Methods:
Cadaveric trochlea were obtained and sectioned into 4 quadrants. Trochleoplasty was performed in each quadrant under one of the following randomized conditions: 3-mm offset with saline irrigation (3Wet), 3-mm offset without irrigation (3Dry), 5-mm offset with irrigation (5Wet), or 5-mm offset without irrigation (5Dry). A 3 × 8-mm strip of cartilage was obtained from the center of each quadrant and from an 8-mm control area. Cartilage samples underwent chondrocyte viability staining with calcein-acetoxymethyl and ethidium homodimer-1. Confocal imaging was performed, and viability across treatment and control groups was compared.
Results:
Eight cadaveric trochlea were obtained from 5 male and 2 female donors (mean age, 26.4 ± 5.6 years). Trochleoplasty was performed at a mean of 25.3 ± 1.3 days from donor death on 5 right and 3 left trochlea. On analysis, control cartilage viability (75.3% ± 12.9%) was greater than those for 5Dry (60.4% ± 9.3%; P = .001) and 3Dry (63.2% ± 13.4%; P = .002). Cartilage viabilities for 5Wet (70.5% ± 11.0%; P = .15) and 3Wet (66.1% ± 10.9%; P = .09) were not significantly different from that of the control. No other intergroup differences were seen.
Conclusion:
Saline irrigation mitigates chondrocyte-induced thermal necrosis when performing trochleoplasty in this cadaveric model.
Clinical Relevance:
Saline irrigation should be used when performing a trochleoplasty, while offset of the trochleoplasty bur does not have an effect on cartilage viability.
Trochlear dysplasia modifies patellofemoral kinematics, decreasing contact area and elevating contact pressures, which together undermine patellofemoral joint stability.1,8,10,21,24,26,31 Trochleoplasty can be used to treat patellofemoral instability in cases of severe trochlear dysplasia. Multiple trochleoplasty techniques have been developed,3,7-9,14,21,27 all sharing the same conceptual foundation: deepening the trochlear groove and correcting dysplastic lateral convexity. This helps to address the osseous root of instability in these patients, creating a path that is conducive for patellar tracking through flexion and extension.
Osteoarthritis is a known complication of trochleoplasty, with ranges from 0% to 82% having been reported in the literature.20,25,32 The wide discrepancy is likely secondary to the utilization of different measures of osteoarthritis, although osteoarthritis rates after trochleoplasty are comparable to those of trochlear dysplasia–induced osteoarthritis.16,18 Chondrocyte viability can be an important marker of osteoarthritis, and it is known to be indicative of success for cartilage restoration procedures including osteochondral allograft transplantation. 6 When performing a recession-wedge trochleoplasty, a high-speed bur is used to develop cartilage and subchondral bone flaps to shape the trochlea. Although the recession-wedge technique is thought to spare trochlear cartilage, excessive burring of subchondral bone could have necrotic effects on the overlying articular cartilage. Elias et al 12 found increased chondrocyte death at the periphery of osteochondral allograft plugs after harvest, believed to be secondary to thermal necrosis from heat generated when reaming. Reaming submerged in water mitigated this effect and resulted in normal cartilage viability. In the lone study to evaluate chondrocyte viability after trochleoplasty, Schöttle et al 28 found 3 patients to have normal cell distribution on histology and minimal chondrocyte death at 9 months after thin-flap trochleoplasty. No comparative studies exist regarding chondrocyte viability after trochleoplasty, and there are no data on chondrocyte viability after recession-wedge trochleoplasty specifically.
This study aimed to quantify the chondrocyte viability of the trochlea after recession-wedge trochleoplasty and evaluate the effect of irrigation during osseous burring of trochleoplasty. Additionally, this study assesses the effect of bur offset on chondrocyte viability after trochleoplasty. We hypothesized that thermal necrosis would be induced by burring and would be mitigated with saline irrigation.
Methods
Trochleoplasty and Cartilage Specimen Harvesting
Before initiation of the study, institutional review board exemption was obtained given the use of de-identified, clinical-grade cartilage specimens. Eight fresh cadaveric human distal femurs were obtained from JRF Ortho. For each femur, the trochlea was divided into 4 quadrants and 1 of the following groups was randomized to each quadrant (Figure 1): 5-mm offset without irrigation (5Dry), 5-mm offset with irrigation (5Wet), 3-mm offset without irrigation (3Dry), and 3-mm offset with irrigation (3Wet). An Arthrex Marking Hook for trochleoplasty and a 2.9-mm bur were used to complete the procedure. Irrigation was performed using a bulb syringe, applying a steady stream of saline for the duration of the trochleoplasty in the designated quadrants. Additionally, a control 3 mm–wide strip of cartilage was harvested from the center of the trochlea. Trochleoplasty was performed using the modified recession-wedge technique. 7 First, a bur with the determined offset was used to perforate the femur in a postage stamp configuration. The perforations were then connected to create a malleable flap. This process was then repeated in each quadrant in a randomized fashion.
A distal femur demonstrating 4 quadrants that were randomized to testing groups. One 8-mm plug was obtained from each quadrant (green), and a control cartilage strip was harvested from the center of the trochlea (red). C, control.
One 8-mm full-thickness cartilage plug was harvested from the center of each trochleoplasty flap using an 8-mm skin biopsy punch. Then, 3 mm–wide rectangular strips of cartilage were excised from each plug, resulting in an 8 × 3-mm cartilage sample for each testing group. Cartilage explants were placed in 15-mL conical tubes containing 5 mL of serum-free culture media before viability staining.
Chondrocyte Viability and Confocal Analysis
Chondrocyte viability of samples was analyzed using confocal microscopy. The cartilage samples were stained using calcein-acetoxymethyl (AM) and ethidium homodimer-1 dye (Molecular Probes/Invitrogen) and were incubated for 60 minutes at 37°C. After incubation, each cartilage sample was placed on a glass microscopy slide and visualized using fluorescent confocal microscopy (Figure 2). Microscopy settings from a previous chondrocyte viability confocal protocol were utilized, with ×10 magnification and green and red laser wavelengths at 488 nm and 561 nm, respectively. 12 Slight corrections to wavelengths were made as necessary to optimize chondrocyte visualization. An image best depicting the 8-mm cartilage was acquired, and ImageJ (National Institutes of Health) was utilized for calculation of the percentage of live cells across the entire sample.
Live/dead image of a full-depth cartilage sample using confocal microscopy with the articular surface on the left. Calcein-acetoxymethyl stains live chondrocytes green, while ethidium homodimer-1 stains dead chondrocytes red. The red bars each indicate 1 mm.
Statistical Analysis
A priori power analysis using an alpha of 0.5 found that a minimum sample size of 5 for each group was needed to obtain a power of 0.80 based on a previous study evaluating chondrocyte viability in osteochondral allograft transplantation. 12 All data analysis was performed using RStudio (Posit). A Shapiro-Wilk test was used to assess for normality of groups. Given the presence of normal data and small sample size, paired t tests were used to compare each group with the control sample. Additionally, a paired t test was utilized to compare 5Dry and 3Dry groups and 5Wet and 3Wet groups to assess for the effect of bur depth on chondrocyte viability. A P value <.05 was considered statistically significant.
Results
Trochleoplasty was performed on 8 distal femoral condyles. Donor characteristics are provided in Table 1.
Donor Characteristics a
Values are presented as mean ± SD or n (%).
Compared with control samples (75.3% ± 12.9%), the viability of 3Dry (63.2% ± 13.4%; P = .002) and 5Dry (60.4% ± 9.3%; P = .001) samples was significantly decreased (Figure 3). There were no differences in chondrocyte viability between control and trochleoplasty samples performed under the 3Wet (66.1% ± 10.9%) or 5Wet (70.5% ± 11.0%) conditions. To assess for the effect of bur depth on chondrocyte viability, viability was compared between 5Dry and 3Dry conditions and 5Wet and 3Wet conditions. There were no significant differences seen in either of these comparisons (P = .64 and P = .31, respectively).
Chondrocyte viability measured as a percentage of live cells. Viability significantly decreased after trochleoplasty was performed under the 3Dry (P = .002) and 5Dry (P = .001) conditions compared with the control. There was no difference in viability after trochleoplasty under the 3Wet (P = .09) and 5Wet (P = .15) conditions compared with the control. Significant P values are presented in bold.
Discussion
The primary objective of this study was to quantify the effect of bur offset and saline irrigation on chondrocyte viability after recession-wedge trochleoplasty. The most significant findings of the current study were that when performing recession-wedge trochleoplasty, the use of 3-mm and 5-mm offset burs resulted in a statistically significant decrease in chondrocyte viability. Notably, however, this study demonstrated that this risk was mitigated with the use of simultaneous saline irrigation.
Trochleoplasty is a technically challenging procedure that is undertaken to correct high-grade trochlear dysplasia in the setting of patellar maltracking.4,5,8,11,28 Several different surgical techniques for trochleoplasty have been described to improve patellofemoral kinematics, including Dejour sulcus-deepening trochleoplasty, elevation trochleoplasty of the lateral femoral condyle, Bereiter thin-flap deepening trochleoplasty, and recession-wedge trochleoplasty.9,21,33,34 One of the theoretical advantages of the recession-wedge trochleoplasty technique is the reduced risk of chondral injury and necrosis because the trochlear segment is maintained and mobilized as a single osteochondral unit after resection of the subchondral bone, rather than splitting the osteochondral flap to create a new groove. 2 Trochleoplasty has generally been supported in the literature to yield good mid- to long-term clinical outcomes and low rates of recurrent patellar instability.8,19,22,23,25 Despite the encouraging clinical outcomes, concerns exist regarding the potential complication profile unique to this procedure. Of particular note is the potential for iatrogenic damage to the articular cartilage and trochlear necrosis.8,28 These complications remain poorly understood, as it is relatively unknown if patellofemoral arthritis might develop as part of the natural history of the preexisting trochlear dysplasia, or if this process is accelerated in any way after the trochleoplasty procedure. 19 Additionally, secondary necrosis of the trochlea has not been previously reported. 2
There is also a relative paucity of basic science and translational research investigating the effects of trochleoplasty on articular cartilage viability. In the study by Schöttle et al, 28 the authors evaluated cartilage viability and quality after trochleoplasty by performing 2 osteochondral biopsies in 3 patients between 6 and 9 months postoperatively. In the study, 1 biopsy specimen was utilized to evaluate chondrocyte viability, and the other was utilized to histologically assess the cartilage, calcified cartilage, and subchondral bone. The authors reported that microscopy demonstrated almost exclusively viable chondrocytes, and the histological assessment demonstrated normal-appearing cartilage, calcified cartilage, and subchondral bone layers. Combined with the respective patient’s clinical and radiological outcomes at short- and midterm follow-up, the authors concluded that trochleoplasty yields a low potential risk for cartilage damage. 2
Despite these encouraging findings regarding the relative safety of the articular cartilage with trochleoplasty procedures, the potential risk of mechanical and thermal injury to osteocyte and chondrocyte viability has been demonstrated elsewhere in the orthopaedic literature.12,13,15,17,29,30,35 The use of external cooling and the relative depth of the subchondral osseous recession being performed are 2 different variables that may logically have the potential to affect chondrocyte viability after trochleoplasty. Elias et al 12 and Hafke et al 15 both demonstrated that the use of saline as an external coolant improves chondrocyte viability during the harvest of osteochondral allograft plugs. Notably, in the study by Elias et al, 12 the authors reported that chondrocyte viability was affected deleteriously at both the peripheral and central aspects of the osteochondral allograft plug when harvested under handheld saline irrigation in comparison with that while submerged in normal saline. As relates to the present study, these findings suggest that a relative zone of mechanical or thermal injury to chondrocytes may extend beyond the area in direct contact with the instrumentation. This study similarly demonstrated a protective effect of the use of saline as an external coolant while a bur was used to perform a recession-wedge trochleoplasty. These findings suggest that with the use of saline irrigation as a coolant, 3-mm and 5-mm offset burs, respectively, may be safely used to create relatively different thicknesses of the osteochondral shell during trochleoplasty. The use of saline irrigation represents a simple and easily adopted modality for surgeons to provide further protective effects to the native cartilage while this procedure is performed.
Limitations
One potential limitation of this study is its relatively small sample size. A trend toward decreased chondrocyte viability with the use of a smaller versus larger bur offset was demonstrated that did not reach statistical significance. It cannot be ruled out that with a larger sample size, this trend may have reached statistical significance. Nonetheless, a priori power analysis demonstrated that the current study was adequately powered for us to draw our respective conclusions. It also remains unclear whether or not the statistically significant differences observed in this study would manifest in clinically significant differences for patients concerning healing of the mobilized osteochondral shell and clinical and radiological outcomes. Despite these limitations, the results of the current study demonstrate that saline irrigation may help minimize the thermal injury to chondrocytes and the underlying subchondral bone. These findings are of clinical relevance as they represent a simple modality that surgeons may utilize intraoperatively when performing a trochleoplasty to help facilitate clinical healing of the mobilized osteochondral shell and improve clinical outcomes for patients. Further basic science and translational research should continue to evaluate and implement other technical modifications that may aid in minimizing the risk of injury to the cartilage, calcified cartilage, and subchondral bone layers and further ensure safety with this procedure.
Conclusion
Saline irrigation mitigates thermal injury to chondrocytes when performing recession-wedge trochleoplasty utilizing bur offsets of 3 and 5 mm. There may be worsened chondrocyte viability in association with the 3-mm offset, but further studies are necessary to elucidate this. Future studies should also evaluate the clinical effect of viability on outcome in the setting of trochleoplasty.
Footnotes
Submitted December 8, 2024; accepted February 27, 2025.
One or more of the authors has declared the following potential conflict of interest or source of funding: This research was made possible through the support of JRF Ortho. A.B.Y. has received consulting fees from AlloSource, JRF Ortho, and Stryker; and holds stock or stock options in Patient IQ, Sparta Biomedical, and Icarus. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.
