Three dimensional CT-based virtual patellar resection in female patients undergoing total knee replacement: a comparison between tendon and subchondral method

Relationships between position of patellar ridge high point and morphology of resected surface for patellar resurfacing in total knee arthroplasty

Background

Reproducing the native patellar ridge high point while maximizing osseous coverage is important for the success of patellar replacement, but it cannot always be achieved simultaneously. This study aimed to thoroughly investigate the relationships and their influencing factors between the positions of the high point of patellar ridge (HPPR) and the morphology of the patellar resected surface.

Methods

Four hundred seventy-three patients (265 men, 208 women) aged 18 to 50 years with knee injuries before arthroscopy were retrospectively collected for this cross-sectional study. Computed tomography (CT) and magnetic resonance imaging (MRI) were used to construct 3D computer models of the patella and patellar cartilage. The morphometric characteristics of the patellar cut after virtual resection and the HPPR position relative to the patellar cut centre were measured and analyzed.

Results

The medial displacements of the HPPR were positively correlated with Wiberg's classification and index (all P<0.001). The mean values of HPPR's medial displacements were 0.15 of the medial width of patellar cut, and 93.2% of all patella ranged from 0 to 0.3. When the implant's apex were placed at 0.15 of the medial width of patellar cut medialized, the proportion of implant placement errors within 1 mm of the native high point was 12% more in female patella (P=0.01), and 7% more in all patella (P=0.03) than 3 mm medialized.

Conclusions

Wiberg's system can roughly predicted the medial-lateral position of the HPPR. The HPPR was mainly medially located at the 0.15 of the medial patellar width approximately, and 15% medialized of the implant's apex can better reproduce the native patellar high point than 3 mm medialized. The current results provide basic data for patellar implant selection, preoperative planning, and implant design to reproduce the native patellar high point better while maximizing osseous coverage for patellar resurfacing.

Clinical and radiologic outcomes of two patellar resection techniques during total knee arthroplasty: a prospective randomized controlled study

PURPOSE

A cutting guide technique for patella resurfacing in total knee arthroplasty was expected to result in less patellofemoral syndromes. The aim of this study was to identify differences in the patellofemoral function, clinical outcomes, and radiographic parameters between the freehand and cutting guide patellar resection techniques in patients undergoing total knee arthroplasty.

METHODS

A prospective randomized controlled trial was conducted. The study was registered in a public trials registry (International Standard Randomized Trial No. NCT02268097). One-hundred total knee arthroplasties in 100 patients were randomly allocated into one of the two groups, and their results were followed for a mean of 28 months (range, 18 to 38 months) in a double-blind (both patient and evaluator), prospective study. Evaluation was performed by an independent observer using patellofemoral functional capacity, the Knee Society clinical rating system, the Western Ontario and McMaster Universities Osteoarthritis Indices, and radiographic examination.

RESULTS

In total, 14% of the patients were lost to follow-up. There was no difference in the incidence of anterior knee pain between the two groups. No patients received or required revisions. There was a significant difference in the outliers of lateral patellar tilt between the freehand and cutting guide groups (> 10°) (p = 0.036); however, the mean value of lateral patellar tilt did not differ significantly. There were no differences between groups with respect to the 30 seconds stair climbing test, complications, the Knee Society clinical rating system, the Western Ontario and McMaster Universities Osteoarthritis Indices, patient satisfaction, physical examination, hip-knee-ankle angle, lateral patellar displacement, or the Insall-Salvati ratio. Meanwhile, gender, age, weight, height, body mass index, pre-operative Knee Society scores, and pre-operative range of motion were not found to be related to the development of anterior knee pain.

CONCLUSIONS

Cutting guide technique group did not yield lower incidence of anterior knee pain. More outliers of lateral patellar tilt were observed in the freehand technique group. Overall, all patients in both groups had identical results in terms of patellofemoral functional capacity, clinical outcomes, and other radiographic results.

Comprehensive assessment of patellar morphology using computed tomography-based three-dimensional computer models

BACKGROUND

The objectives of this study were to assess patellar morphology using computed tomography-based three-dimensional computer models and to determine the utility of the subchondral method for patellar resection in total knee arthroplasty (TKA).

METHODS

Overall, 120 subjects (60 males, 60 females) from 20 to 50 years old were included. Computer tomography images were used to construct 3D computer models of 240 knees. An anthropometric analysis of variance was used with the models to detect differences between the sides, age groups, and genders.

RESULTS

Based on the available numbers, there were significant gender differences in the patellar length, width, and thickness even with strict control for the height and weight of the patients. The average patellar width/thickness ratio was 1.95, regardless of gender, and there was a good correlation between the patellar width and thickness (male: r=0.68, p<0.01; female: r=0.75, p<0.01). After using the subchondral method to virtually resect the patellae, the mean thickness for males and female was 14.0mm and 12.3mm, respectively. The proportion of the residual bony thickness that was less than 12 mm was 5.83% (seven cases) in the male group and up to 42.5% (51 cases) in the female group. There was excellent intra-observer reliability and inter-observer reliability regarding the dimensional measurements in this study.

CONCLUSIONS

A robust method of measuring and virtually resecting the patella was established. The anthropometric dimensions of this study could provide basic data for guiding surgical management of the patella in TKA and are useful in designing patellar implants.

CLINICAL RELEVANCE

The anthropometric patellar information is essential for surgeons to perform patellar resurfacing in TKA.