For the time period of August 2017 to August 2021, patients between 14 and 50 years of age were identified via Current Procedural Terminology codes specific to OCA procedures (code 27415) and International Classification of Diseases , Tenth Revision , codes for chondromalacia patellae (M22.41 and M22.42), then filtered for a single, high-volume patellofemoral practice surgeon’s cases. All allografts were preserved with the MOPS technique. Patients with concurrent OCA transplantation (trochlea or tibiofemoral compartments) were included. Patients with concomitant tibiofemoral disease also were included in the study and were treated at the time of surgery to eliminate any source of pain. However, the concomitant tibiofemoral disease was not considered the primary issue for these patients. Exclusion criteria consisted of open physes, previous OCA transplantation, or less than 2 years of follow-up. Any postoperative PROs acquired sooner than 2 years from the date of the OCA transplantation surgery were excluded. The indications for osteochondral allograft to the patella were patients with grade 3 to 4 articular cartilage injuries to the patella of at least 2.25 square centimeters in diameter. Patients with or without bone defects were included. All patients failed at least 6 months of nonoperative treatment. Retrospective in design, this study received institutional review board approval (Thomas Jefferson University; study #21E.989) approval.

Demographic variables were collected from the electronic medical record along with previous ipsilateral surgical procedures. The primary pathology, i.e., the diagnosis that contributed to the cartilage defect, was also collected and categorized as follows: lateral patellar instability (LPI), as defined by lateral dislocations and/or subluxations, juvenile osteochondritis dissecans (OCD), as defined by an atraumatic unstable osteochondral fragment, or patellofemoral (PF) chondrosis, defined by nontraumatic PF chondral defects in the absence of reported subluxations or dislocations. Preoperative cartilage assessments included Outerbridge Scores as determined at the time of surgery and the intraoperative dimensions of cartilage defects. Donor allograft characteristics also were recorded, including donor age, graft storage time, graft diameter, and graft area.

Operative notes, datasheets, and images were all reviewed to confirm procedure details. All patients underwent diagnostic arthroscopy to confirm the severity and size of the cartilage defect before the ordering of a size-matched allograft. The cartilage status of all knee compartments was assessed routinely using a marked probe to measure lesions. Indications for proceeding with the second stage was the presence of focal cartilage defects >2 cm ² in active individuals who lacked advanced osteoarthritis.

OCA transplantation was performed with any additional indicated procedures such as tibial tubercle osteotomy (TTO) or medial patellofemoral ligament reconstruction (MPFLR), often through a medial parapatellar arthrotomy except in instances in which an isolated lateral retinacular lengthening was performed with the OCA, for which a lateral parapatellar arthrotomy was used. Cartilage defects were measured ( Fig 1 ) then removed en bloc with the subchondral bone using the hollow core reamer. The desired depth of bone to be removed is approximately 4 mm, with strict attention to ensure no less than 4 mm of bone was present at any point along the perimeter of the plug. The allograft plug was then harvested from the donor and shaped to match the depth of the first plug. The bony undersurface of the allograft plug was perforated with a 2.0-mm drill bit without violating the subchondral bone ( Fig 2 ). The allograft plug was then aligned in the patient’s harvest site and impacted in place ( Fig 3 ).

A left knee after a medial parapatellar arthrotomy has been made. The patella has been everted, and a guide pin has been placed through the center of the defect. The sizing tube is placed over the guide pin to determine the size of the hollow core reamer needed for the removal of the entire defect. (PT, patellar tendon.)

Bony under surface of the donor allograft plug while it is being held in place by a circumferential clamp. With a 2.0-mm drill bit, the bony undersurface is perforated without penetrating the subchondral bone in order to provide additional channels for the influx of native bone marrow elements.

A left knee after a medial parapatellar arthrotomy has been made and an allograft for a medial patellofemoral ligament (MPFL) reconstruction has already been fixated to the patella. The MPFL reconstruction is fixed to the medial side of the patella, which is everted in the image in order to display the articular surface. The final appearance of the osteochondral allograft (OCA) plug after impaction is demonstrated. (PT, patellar tendon; TT, tibial tubercle.)

The postoperative protocol for isolated OCA of the PF joint (patella and or trochlea) included protected weight-bearing as tolerated with crutches in a hinged knee brace locked in extension for 6 weeks. Full range of motion (ROM) was encouraged immediately at postoperative day 1. If a TTO was performed, the patient was non−weight-bearing for the first 6 weeks. If medial femoral condyle or lateral femoral condyle OCA was performed, the patient was toe-touch weight-bearing over the first 6 weeks. At the 6-week time point, all patients were permitted to weight-bearing as tolerated with crutches and instructed to wean off the crutches over the next 6 weeks. There were no ROM restrictions imparted at any point. In all patients, impact exercises and activities were permitted after 6 months.

Postoperative magnetic resonance imaging (MRI) scans, when available, were reviewed by 2 blinded raters (C.A.S. and R.T.K.) to determine Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) 2.0 scores for patellar lesions in accordance with previously established methods. MRIs were not performed in response to the patient’s symptoms but were routinely performed from 9 months to 1 year postoperatively to evaluate graft incorporation for research purposes. Tibial tubercle-trochlear groove distances were measured on all patients using preoperative MRIs, when available.

PRO measures were collected using the Outcomes Based Electronic Research Database software (Universal Research Solutions; www.oberd.com ). PROs assessed included International Knee Documentation Committee Subjective Knee Form (IKDC), Knee Injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS JR), Short-Form 12 Physical Health Survey (SF-12 PH), and Veterans RAND 12 Physical Health Survey (VR-12 Physical). The IKDC, KOOS JR, SF-12 PH, and VR-12 Physical thresholds for achieving MCID was defined as an increase of 18.75, 18.76, 11.90, and 13.56, respectively (0-100).

When appropriate, paired sample t tests were used to assess for changes in preoperative and postoperative PRO scores. To assess the normality of the distribution, a Kolmogorov-Smirnov test was used. Independent t tests were used to assess differences amongst nonpaired continuous variables. Cohen d was calculated to determine effect sizes along with 95% confidence intervals. χ ² and Fisher exact tests were used to analyze categorical data. Pearson correlation coefficients (r) was used for correlations. Subanalyses were conducted for primary pathology and bipolar osteochondral allografting (kissing lesions). For all statistical testing, P values <.05 were deemed to be significant. Analysis was conducted using IBM SPSS Statistics, Version 29.0.1.0.

In total, 37 knees among 34 different patients were identified. Nine knees were excluded for incomplete records or inadequate follow-up, leaving 28 knees in 26 patients. Twenty-two knees belonged to female patients (78.6% of all knees). The mean follow-up was 3.6 ± 1.4 years (range 2.3-5.8 years) after OCA implantation. The mean age was 31.0 ± 10.3 years and the mean BMI was 30.0 ± 5.6. Eighteen knees (64.3%) presented with lateral patellar instability, 9 (32.1%) with PF chondrosis, and 1 (3.4%) with patellar OCD. Six (21.4%) patients had concomitant tibiofemoral disease.

All knees had patellar lesions with Outerbridge Scores of either 3 (n = 5) or 4 (n = 23) at the time of the staged diagnostic arthroscopy, and 19 (67.9%) had 1 or more additional femoral cartilage defects with an Outerbridge score of 3 or greater. Patellar and femoral defects with Outerbridge scores of 3 or greater are mapped in Figure 4 A and B. The area of patellar chondral defects was 4.5 ± 1.9 cm ² (range 2.3-7.5 cm ²). Twelve knees (42.9%) had a bipolar “kissing” defects within the trochlea, with the average trochlear defect area in these patients being 4.1 ± 3.7 cm ² (range 1.5-15 cm ²).

(A) The locations of patellar articular defects that were Outerbridge 3 or 4. All patellar defects underwent osteochondral allograft (OCA) transplantation. The medial facet (MF) was most frequently involved, followed by the central ridge (CR), the lateral facet (LF) and full-width defects. (B) The location of Outerbridge 3 or 4 chondral defects in the femur that concomitantly underwent OCA transplantation. Trochlear defects were location the proximal lateral trochlear shoulder (LTS), the lateral femoral condylar sulcus (LFCS) at the terminal lateral trochlear facet, the extension bearing surface of the lateral femoral condyle (LFC), the central trochlea (CT) and the medial femoral condyle (MFC). The trochlea is outlined in hashmarks, and the respective number of patients for each defect location are listed inside the circles along with the percentage this represents among all patients.

All allografts (100%) were preserved using the MOPS technique. The average graft storage time was 51.2 ± 5.6 days, with an average donor age of 24.3 ± 5.3 years. The mean diameter of the allografts harvested for patellar implantation was 21.3 ± 4.3 mm.

A total of 18 (64.3%) knees underwent previous surgeries distinct from staging arthroscopy. No knees had previous osteochondral allografting, autologous chondrocyte implantation, matrix-induced autologous chondrocyte implantation, or particulated juvenile articular cartilage transplantation. However, 4 (14.3%) had received previous microfracture of the patella. For the index study procedure, 16 (57.1%) knees underwent unipolar patellar OCA transplantation, whereas 12 (42.9%) bipolar transplantations for “kissing” lesions. Eleven knees underwent a TTO (concomitant or previous), comprising 61.1% (11/18) of the knees with LPI knees. No knees with PF chondrosis or OCD had a previous or concomitant TTO. Procedures performed concomitantly with OCA are listed in Table 1 .

Paired t testing for preoperative and postoperative PRO scores is listed in Table 2 . Postoperative PROs were acquired on average 3.4 ± 1.6 years after OCA transplantation. Outcome scores were significantly greater postoperatively compared with preoperatively for IKDC, KOOS Jr, SF12-PH, and VR12-Physical. Subgroup analyses shown in Figure 5 display the mean difference between the preoperative PROs and postoperative PROs for LPI, PF chondrosis, and unipolar and bipolar OCAs. Knees that received bipolar OCA had larger improvements in IKDC scores than patients who had unipolar OCA transplantations (54.6 ± 20.5 vs 24.1 ± 17.9; P =.007). The rates of achieving MCID for IKDC, KOOS JR, SF-12 PH and VR-12 Physical were 70.6%, 73.5%, 73.5%, and 61.8%, respectively.

Table 2

Pre- and Postoperative Pairwise PRO Comparisons: All Patients

Outcome Score	Preoperative Mean (±SD)	Postoperative Mean (±SD)	Mean Difference (95% CI)	Effect Size ∗ (95% CI)	P Value
IKDC	36.6 (14.5)	71.9 (20.0)	35.4 (23.9-46.8)	1.49 (0.82 to 2.14)	<.001
KOOS Jr	49.8 (13.4)	77.5 (22.4)	27.7 (13.2-42.2)	1.16 (0.43 to 1.85)	.001
SF-12 PH	33.5 (10.8)	45.3 (11.7)	11.8 (4.8-18.7)	0.794 (0.281 to 1.29)	.002
VR-12 Physical	34.5 (7.8)	49.6 (14.4)	15.2 (7.5-22.8)	0.923 (0.39 to 1.44)	<.001

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