A retrospective review was conducted of all adult patients who underwent patellar cartilage surgery with either aSCD or NoSCD between August 2013 and December 2022. Institutional review board approval was obtained, and all procedures were performed by a fellowship-trained sports medicine orthopaedic surgeon (K.J.E.). Inclusion criteria consisted of patients treated for isolated patellar cartilage injuries using an allograft cartilage scaffold, with or without subchondral drilling, and a minimum 2-year follow-up. Patients were excluded if they underwent any previous cartilage procedure (aside from shaving chondroplasty), concurrent meniscal surgery, anterior cruciate ligament reconstruction, or distal femoral osteotomy at the time of their cartilage surgery. Of note, patients who underwent tibial tubercle osteotomy (TTO) were still included in the study, as this was not considered a strict inclusion/exclusion criterion.

Demographic data, operative details, scaffold type, chondral defect size, and osteoarthritis grade were collected through a review of patient charts and radiographs (sunrise and lateral views). Osteoarthritis severity was graded using the Kellgren-Lawrence classification system, which ranges from 0 to 4 in increasing severity. ^, The Caton-Deschamps index was also recorded to assess patellar height. Both radiographic measurements were performed by K.J.E., who was not blinded to the study design.

Patient-reported outcome measures (PROMs), including the subjective International Knee Documentation Committee (IKDC) and Lysholm scores, were collected at 4 time points: preoperatively, 6 months postoperatively, 1 year postoperatively, and at final follow-up via face-to-face or e-mail. ^, Additional outcomes included complications, specifically rates of arthrofibrosis requiring a manipulation under anesthesia with or without lysis of adhesions, cartilage overgrowth requiring arthroscopic debridement, conversion to total knee arthroplasty, and infection. Arthrofibrosis was specifically defined as a flexion contracture >10° or an inability to flex beyond 70° at 6 to 8 weeks postoperatively, or persistent loss of ≥5° of extension or flexion <110° at final follow-up. Cartilage overgrowth was diagnosed via second-look arthroscopy and when the cartilage fill was above the level of the native cartilage.

Patients in the aSCD group had particulated allograft cartilage hydrated with platelet-rich plasma (BioCartilage; Arthrex) or flexible osteochondral allograft (Cartiform; Arthrex) as the extracellular matrix scaffold, while patients in the NoSCD group either had Cartiform or PJAC (DeNovo Zimmer Biomet) as the extracellular matrix scaffold. PJAC consists of minced juvenile hyaline cartilage, while BioCartilage is derived from minced adult articular cartilage. Cartiform is composed of articular cartilage on a thin, perforated bony base, which enhances flexibility and integration. Given that the purpose of BioCartilage is to act as a scaffold over a microfractured defect, this option was considered only in patients in the aSCD group and not in the NoSCD group. Cartiform could be used in both cases. The technique for PJAC does not require microfracture and can be placed on top of the subchondral bone after proper preparation. Overall, no strict criteria dictated which technique was performed. Initially, the senior author (K.J.E.) employed aSCD with BioCartilage and Cartiform predominantly in the patellofemoral (PF) joint. However, as the outcomes in the aSCD group failed to meet the senior author’s clinical expectations, alternative approaches, including treatment without subchondral drilling using Cartiform and PJAC, were explored. Over time, it became evident that avoiding subchondral drilling in the PF joint resulted in superior outcomes, leading the senior author to discontinue microfracture for PF joint defects entirely, and in turn, the NoSCD and aSCD were not contemporaneous. Regarding scaffold selection, there was no strict indication for the choice of the scaffold, as it depended on institutional availability. Thus, the choice of treatment was based on intraoperative findings, a discussion with the patient, and clinical judgment at the time of surgery.

All procedures were performed with the patient in the supine position, utilizing a nonsterile tourniquet applied around the proximal thigh, under general anesthesia, and with a femoral nerve block. A diagnostic arthroscopy was conducted through standard anteromedial and anterolateral portals to assess the chondral injury and evaluate any associated ligamentous or meniscal pathology. Once the cartilage damage had been assessed arthroscopically, the arthroscopic equipment was removed from the knee. A parapatellar arthrotomy was performed by making an incision either medially or laterally, depending on the location of the injury. Once the defect was clearly visualized and measured with a ruler, a curette was used to remove any remaining cartilage, scar tissue, and the calcified cartilage layer while creating 90° margins around the defect. Vertical walls were then prepared by trimming loose cartilage edges with a No. 15 blade, and the prepared defect was measured. Next, based on the study group, patients underwent one of the following procedures: subchondral drilling with BioCartilage augmentation, Cartiform augmentation, or direct scaffolding using Cartiform or PJAC without subchondral drilling.

The indication for TTO was a tibial tubercle–trochlear groove distance ≥20 mm or a Caton-Deschamps Index (CDI) ≥1.4. Anterior medialization was performed with a 45° osteotomy cut, leaving a thin distal shingle and translating the tubercle ∼1 cm medially to correct the tibial tubercle–trochlear groove to ∼10 mm. For distalization (patella alta), a complete osteotomy was performed, removing ∼1 cm of tibia distal to the tubercle to correct the CDI to ∼1.1. In all cases, fixation was achieved with 2 headless screws.

Once the bony bed was prepared, a subchondral drilling of the entire bed was performed using a 1.6-mm K-wire on power. Each hole was 3 to 4 mm from each other, and the depth of each was about 8 to 9 mm. Irrigation was used to minimize thermal necrosis. For BioCartilage implantation, 1 mL of prepackaged BioCartilage was combined with 1 mL of previously prepared leukocyte-poor platelet-rich plasma in the Arthrex Mixing and Delivery Syringe. The microfracture site was dried in preparation for the BioCartilage. The BioCartilage/platelet-rich plasma mixture was then injected into the defect through the Tuohy needle, with careful attention to avoid overfilling the defect, keeping the level below the surrounding cartilage margin. A Freer elevator was used to smooth the BioCartilage, and fibrin glue was applied over both the defect and the adjacent cartilage. The fibrin glue was allowed to set for 5 minutes. Finally, after removing all instrumentation, compressive force was applied to the knee to contour the BioCartilage against the opposing articular surface.

For patients who underwent subchondral drilling, the procedure was performed as previously described. For patients who did not undergo subchondral drilling, Cartiform implantation was performed immediately. The Cartiform allograft was placed directly over the defect, ensuring proper alignment of the osseous side with the subchondral bone, and then trimmed to precisely fit the lesion. Then, 4-0 Vicryl (Ethicon) sutures were passed in a mattress fashion at the anticipated anchor sites. A drill was used to prepare the subchondral bone at the superolateral margin of the defect for the insertion of a 2.5-mm mini-PushLock anchor (Arthrex). This process was repeated at the superomedial and inferior margins to secure the graft with 3 anchors, taking care to avoid overtensioning. Finally, fibrin glue was applied over the graft and allowed to set for 5 minutes.

Patients undergoing PJAC did not receive subchondral drilling. After the bed was prepared, a thin layer of fibrin glue was placed at the base of the defect. One package of DeNovo NT graft was allocated for every 2.5 cm ² of defect area. The nutrient medium was aspirated, and the particulated cartilage pieces were transferred evenly on top of the thin layer of fibrin glue. A second layer of fibrin glue was placed over the PJAC and allowed to dry for 5 minutes.

Both groups followed an identical rehabilitation protocol postsurgery. Each patient was placed in a postoperative brace locked in extension for the first 2 weeks following surgery and weight bear as tolerated. Following this, patients were allowed to be 50% weightbearing with the knee locked in extension from weeks 2 to 6. After 2 weeks, the brace was unlocked, and patients were able to begin passive knee flexion up to 90° when not weightbearing. However, the brace was locked in extension for the first 6 weeks while weightbearing. The reasoning for limiting range of motion initially was to allow for the soft tissue envelope to subside and begin healing. Formal physical therapy began at 2 weeks postoperatively and focused on passive range of motion and quad activation. After 6 weeks, patients were weaned out of their brace and off their crutches. Jogging was allowed to begin at 4 to 6 months, and return to sports typically was allowed at 7 to 9 months after surgery.

Descriptive statistics were calculated for all variables, including patient demographics, patient-reported outcomes, and complications. Normality of continuous variables was assessed using the Shapiro-Wilk test. Comparisons between the aSCD and NoSCD groups were made using either the unpaired Student t test or χ ² test, with a significance level of.05. Additionally, for categorical data and nonnormally distributed data, a nonparametric Mann-Whitney U test was performed. The minimal clinically important difference (MCID) was determined using the distribution-based method, defined as half the standard deviation of the change in outcome scores from preoperative to 1-year follow-up and preoperative to final follow-up. MCID thresholds were calculated separately for the IKDC and Lysholm scores. Threshold analyses were then performed to evaluate the proportion of patients in each cohort who exceeded the MCID, and these proportions were compared using the χ ² test to identify any clinically meaningful differences between groups. Statistical analyses were conducted using R software (version 4.2.3; R Foundation for Statistical Computing) and Excel (Microsoft).

A total of 65 patients were included in the study, with 31 patients undergoing aSCD and 34 undergoing NoSCD ( Fig 1 ). The average follow-up period was 52.7 months for the aSCD group (range, 24-88 months) and 48.2 months for the NoSCD group (range, 24-73 months) ( Table 1 ). There were no significant differences between the aSCD and NoSCD groups in terms of age or body mass index, and both groups were predominantly female (aSCD: 80.6%; NoSCD: 76.5%). The median size of the cartilage defect was comparable between the groups (aSCD: 3.00 cm ² vs NoSCD: 3.50 cm ²; P =.359). TTO was performed in 87.1% of aSCD patients and 91.2% of NoSCD patients ( P =.897). There were significant differences in the type of extracellular matrix used, with all 3 scaffolds—BioCartilage, Cartiform, and PJAC—showing a statistical difference between the 2 groups ( P <.05).

Patient flowchart.

At the preoperative time point, there were no significant differences in the IKDC scores ( P =.791) and Lysholm scores ( P =.259) between the aSCD and NoSCD groups ( P =.791) ( Table 2 ). At the 1-year postoperative time point, the NoSCD group had significantly higher IKDC scores (83.0 vs 74.0, P <.001) and Lysholm scores (81.5 vs 74.0, P <.001) compared to the aSCD group. This trend persisted at the final postoperative time point, with the NoSCD group again showing significantly higher IKDC scores (81.0 vs 74.0, P <.001) and Lysholm scores (83.0 vs 77.0, P <.001). aSCD was independently associated with lower final IKDC (β =–8.97; P =.001) and Lysholm scores (β =–12.71; P <.001), and the BioCartilage scaffold predicted a significantly higher Lysholm score compared with Cartiform (β = +8.50; P =.007) ( Table 3 ).

Table 2

Patient-Reported Outcome Scores

Characteristic	aSCD (n = 31)	NoSCD (n = 34)	P Value ∗
IKDC
Preoperative	51.0 (45.0-53.0)	53.0 (45.0-55.0)	.791
6-month postoperative	65.0 (61.0-74.0)	67.0 (64.0-72.0)	.825
1-year postoperative	74.0 (71.0-78.0)	83.0 (81.0-86.0)	<.001
Final postoperative	74.0 (70.0-77.0)	81.0 (79.0-81.0)	<.001
Lysholm
Preoperative	55.0 (51.0-59.0)	48.0 (45.0-54.0)	.259
6-month postoperative	64.0 (57.0-68.0)	69.0 (65.0-72.0)	.428
1-year postoperative	74.0 (72.0-79.0)	81.5 (80.0-85.0)	<.001
Final postoperative	77.0 (73.0-80.0)	83.0 (81.0-86.0)	<.001

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