Purpose
To report the safety and efficacy of biointegrative fiber-reinforced implants for tibial tubercle osteotomy (TTO) and perform a cost-benefit analysis.
Methods
Patients treated with TTO for all indications by a single surgeon from May 2017 to July 2024 were retrospectively reviewed. There were no exclusion criteria. In 2023, the surgeon switched TTO fixation from two 4.5-mm metal compression screws to 2 biointegrative, partially threaded 4.0-mm headless compression screws, made of continuous mineral fibers comprised of elements found in natural bone (SiO 2 , Na 2 O, CaO, MgO, B 2 O 3 , and P 2 O 5 ), and bound together by PLDLA [poly (L-lactide-co-D,L-lactide)] (70:30 L:DL) in 50% weight by weight ratio. Postoperative protocols were consistent across fixation types, with full weight-bearing as tolerated in full extension for 6 weeks and range of motion from 0 to 90° allowed immediately. Patients were followed longitudinally for osseous union, recurrent instability, and return to the operating room.
Results
Sixty-two TTOs were analyzed (44 metal, 18 biointegrative); 61.3% of patients were female, and the median age was 23.3 years (interquartile range 22.5). One patient with biointegrative implants underwent irrigation and debridement with implant retention at 9 days postoperatively. Mean follow-up for biointegrative fixation was 1.3 ± 0.4 years (range: 0.5-1.8) and for metal fixation was 3.5 ± 1.8 years (range: 0.4-6.7), P <.001. All patients achieved clinical union by 6 months without differences in time to clinical union ( P =.159). Hardware removal rates differed between metal versus biointegrative groups (29.5 vs 0%, P =.009) but otherwise did not differ for rates of superficial infection (2.3 vs 0%, P =.519) or deep infection (2.3 vs 5.6%, P =.507).
Conclusions
Biointegrative screws are a safe and effective alternative to metal screws for TTO in short-term follow-up. The use of biointegrative fixation may reduce the need for secondary hardware removal procedures commonly reported with 4.5-mm metal screws, albeit at a potentially increased cost to the health system.
Level of Evidence
Level III, retrospective comparative study.
Tibial tubercle osteotomy (TTO) is a well-described surgical treatment option for a broad range of patellofemoral joint disorders. , In clinical practice, the osteotomy is most commonly fixated using 2 or 3 metal compression screws (CS), providing the required fixation strength. When 2 screws are used, they are often larger screws that have been associated with symptomatic hardware. Multiple potential complications can follow metal TTO fixation, including superficial wound infections, skin irritation and necrosis, symptomatic hardware, tibial or tuberosity fractures, nonunion, neurovascular complications, and deep infection, all of which can result in the need for revision procedures and hardware removal. ,
Prominent and symptomatic hardware often results in the need for a secondary removal of hardware (ROH). Bioabsorbable implants purportedly limit the prominence of hardware as they degrade with time. In fixation for TTO, the use of bioabsorbable screws has previously been evaluated biomechanically and showed adequate fixation strength for early mobilization. Further, they have been evaluated clinically in fixation of pediatric tibial tubercle fractures and were found to eliminate the need for hardware removal compared with metal screws. However, bioabsorbable implants for other indications are not without their own distinct complication profile. In the setting of anterior cruciate ligament reconstructions, approximately 10% of patients with bioabsorbable interference screws were found to develop a screw-related problem. Related problems included implant migration, cyst accumulation, and peri-implant osteolysis, which can occur as a result of an acidic microenvironment and foreign body reaction.
Biointegrative mineral fiber-reinforced implants may limit some of these adverse tissue responses , because they are thought to undergo a more gradual biointegration without adverse inflammatory response. Recent evidence suggests that more recent bioabsorbable implants may have lower complication rates than historical alternatives. However, the use of biointegrative mineral fiber-reinforced implants has not been reported for fixation in TTO, and there has been limited reporting on the cost-benefit of such implants. Therefore, the purpose of this study was to report the safety and efficacy of biointegrative fiber-reinforced implants compared with metal screws for TTO and perform a cost-benefit analysis. Our hypothesis was that union rates and outcomes would be similar between fixation types while reducing the need for hardware removal with biointegrative screws, and we projected that the use of biointegrative screws would not increase costs to the health system compared with metal CS because of a decrease in hardware removal rate with biointegrative screws.
Methods
Institutional review board approval was obtained for this retrospective comparative study WCG IRB #U21-10-4593). Patients were included if treated with TTO (Current Procedure Terminology [CPT] code 27418) by the senior surgeon (B.B.) at a private, academic model institution from May 2017 to July 2024. No patients were excluded in an effort to capture the entire complication profile postoperatively for this procedure. The senior surgeon is fellowship-trained in sports medicine with more than 17 years in practice. In 2023, the surgeon switched TTO fixation from 2 metal screws to 2 biointegrative screws.
Patient sex, age, BMI, smoking status, and presence of diabetes were recorded. The tibial tubercle-trochlear groove distance was recorded on preoperative advanced imaging. The indication for surgery was grouped into patellar instability, chondral offloading, or both. Concomitant procedures were recorded.
Postoperatively, patients were followed longitudinally with standard postoperative visits at 2 weeks, 6 weeks, 12 weeks, and 6 months. Radiographs were typically obtained at the 6- and 12-week postoperative visits. Clinical or radiographic union was verified. All patients with biointegrative implants were followed until radiographic union. Clinical union was defined as lack of tenderness to palpation about the osteotomy site. Radiographic union was defined as bridging bone across the osteotomy site on radiographs. Radiographs were evaluated for union by an orthopaedic surgery sports medicine fellow (R.D.). The presence of recurrent patellar instability was evaluated for at all postoperative visits and the time to recurrence was recorded if present. Superficial infection requiring only antibiotics was distinguished from deep infection requiring return to the operating room for irrigation and debridement with or without removal of hardware. All cases of reoperation and their timing were recorded and grouped by irrigation and debridement, revision procedures, or ROH (CPT code 20680). These data were collected retrospectively in a single effort immediately before statistical analysis. Finally, the cost of implants at the study health system were obtained in addition to the median cost for ROH and TTO procedures by CPT code for the year 2024 in both the ambulatory surgical center and hospital facility settings.
Surgical Technique
The patient was placed supine on a standard operating room table. Diagnostic arthroscopy was performed before TTO and intraarticular pathology was treated at that time. For TTO, an 8-cm longitudinal incision was made centered over the tibial tubercle to identify and free the medial and lateral borders of the patellar tendon. The anterior compartment was elevated from the lateral tibia using a Cobb elevator to expose the osteotomy site. A freehand cut at 10-15° was made from medial to lateral across the tibial. The periosteum was left intact at the distal osteotomy and straight osteotomes were used to complete the superomedial and superolateral portions of the osteotomy before completing the distal aspect of the osteotomy. The tibial tubercle was medialized approximately 9 mm, then secured with 2 Kirschner wires at the desired screw location and trajectory. The superior screw path was drilled, then length was measured, and finally tapping and countersinking were performed before metal or bio-integrative screw placement ( Fig 1 ). This process was repeated for the inferior screw and verified under fluoroscopy. For the biointegrative screws, any remaining screw prominence was able to be removed with rongeur until flush with the tibia tubercle. No bone grafting was performed at the osteotomy site.
After tibial tubercle osteotomy (red arrowheads), anteromedialization was held in place with 2 Kirschner wires (A) for cannulated drilling (B) as shown on lateral fluoroscopy of the knee with the patient in the supine position. Tapping of each screw tract was performed (C) for biointegrative compressive screw placement for fixation. After placement, 2 radiolucent tracks can be seen at the site of the inferior and superior biointegrative screws (D).
In 2023, the surgeon switched TTO fixation from using 2 fully threaded, headed 4.5-mm metal CS without washers (Synthes, Warsaw, IN) to using 2 biointegrative, partially threaded 4.0-mm headless CS (Ossio, Caesarea, Israel). These biointegrative implants are made of continuous mineral fibers composed of elements found in natural bone (SiO 2 , Na 2 O, CaO, MgO, B 2 O 3 , and P 2 O 5 ), and bound together by PLDLA [poly (L-lactide-co-D,L-lactide)] (70:30 L:DL) in 50% weight-by-weight ratio.
Postoperative Protocol
Postoperative protocols were consistent across fixation type. Patients were full weight-bearing as tolerated in full extension for 6 weeks, with range of motion from 0 to 90° allowed immediately. At 6-week follow-up, bracing was discontinued and activity advanced with evidence of clinical evidence of patellar stability and evidence of progression toward osseous union. Return to running was allowed beginning at 12 weeks.
Statistical Analysis
Descriptive statistics were generated for the entire cohort and by implant group. Comparisons of continuous data were conducted with t-tests or Mann-Whitney U test for non-normally distributed variables and categorical data with χ 2 or Fisher exact tests. Kaplan-Meier survival plots were created by implant type for time to ROH. Multivariate logistic regression analysis was performed to identify factors associated with ROH using demographics and implant group. Qualitative information related to the postoperative course was analyzed for any complication or reoperation for patients with both implant types for fixation. A cost-benefit analysis was performed to compare the cost to the health system for each method of TTO fixation, taking into account implant costs, the median cost of TTO and ROH by surgical setting, and the removal of hardware rate by implant group. A-priori alpha level was established as P <.05. Statistical analyses were performed using jamovi v2.2.5.0.
Results
Sixty-two TTOs were analyzed (44 metal, 18 biointegrative). There were no exclusions and all were primary TTO. The overall cohort was 61.3% female, with median age of 23.3 years (interquartile range [IQR] 22.5 years) and BMI 25.7 (IQR 5.0). Because of limited numbers in each subgroup, further analysis remained aggregated by sex. Only 1 patient (1.6%) was an active smoker, and no patients had diabetes. Mean follow-up duration was 2.9 ± 1.8 years. Mean preoperative tibial tubercle-trochlear groove was 18.1 ± 3.1 mm. Patients were indicated for TTO for chondral offloading (11.3%), isolated patellar instability (22.6%), or both (66.1%). Concomitant procedures included 22 medial patellofemoral ligament reconstructions, 9 lateral retinacular releases or lengthening, 3 osteochondral allograft transplantation surgery, 5 debridements, 3 chondroplasties, 3 loose body removals, and 1 meniscus root repair. When we compared implant groups, only follow-up duration ( P <.001) and indications for surgery ( P =.013) were significantly different between groups ( Table 1 ). All patients achieved clinical union and clearance for return to activity without restriction by 6 months without differences in time to clinical union between groups ( P = .159), as shown in Table 2 . All biointegrative TTOs achieved radiographic union ( Fig 2 ).
Table 1
Comparison of TTO Fixation Implant Groups
| Characteristic | Metal | Biointegrative | P Value |
|---|---|---|---|
| Age, y (IQR) | 22.4 (20.1) | 2.59 (23.5) | .443 |
| BMI (IQR) | 25.8 (6.1) | 23.9 (4.4) | .092 |
| TT-TG, mm | 17.8 ± 2.9 | 18.9 ± 3.6 | .195 |
| Follow-up, yr (range) | 3.5 ± 1.8 (0.4-6.7) | 1.3 ± 0.4 (0.5-1.8) | <.001 |
| Sex: % female | 61.4% | 61.1% | .985 |
| Indication for surgery, n | |||
| Chondral offloading | 7 | 0 | .013 |
| Patellar instability | 6 | 8 | |
| Both | 31 | 10 | |
| ROH, % | 29.5% | 0.0% | .009 |
| Recurrent instability, % | 13.6% | 0.0% | .099 |
| I&D, % | 2.3% | 5.6% | .507 |
| Revision, % | 4.5% | 0.0% | .358 |
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