The Femur-First Technique for Oxford Medial Unicompartmental Knee Arthroplasty.

Background: Unicompartmental knee arthroplasty (UKA) is a reliable procedure to treat medial compartment knee osteoarthritis (OA). The reported survivorship of UKA has varied in the literature3-7. In part, the higher failure rates of UKA seen in registries could be related to the caseload and experience of the reporting surgeon8. The introduction of techniques that make procedures more reliable, especially in the hands of inexperienced surgeons, can decrease the rate of failure. With the Oxford UKA implant (Zimmer Biomet), the recommended surgical technique involves cutting the tibia first, followed by the femoral preparation. However, a technique that allows for preparation of the femur first, as well as the use of the femoral component as a reference for the tibial cut, may reduce the common technical errors seen with the procedure. We have utilized the femur-first technique in cases of medial Oxford UKA. Description: The femur-first method outlined in the present article does not require any unique instruments beyond what is supplied by the manufacturer. Before beginning, the femoral positional guide needs to be decoupled from its base. To start, the intramedullary guide is introduced approximately 1 cm anterior and medial to the intercondylar notch. Once the femoral osteophytes are removed, the surgeon identifies the center of the femoral condyle and marks it. The posterior tibial cartilage is then removed with a saw to facilitate the placement of the appropriately sized femoral spherical guide. The size of the femoral component is determined by selecting the implant that aligns best with the width of the femoral condyle. The femoral drill guide is detached from its base because there is not enough space for the base, as the tibia has not yet been resected. The decoupled femoral guide is connected to the intramedullary rod, allowing the precise positioning of the femoral component in approximately 10° of flexion relative to the femoral sagittal plane and drilling of the 2 peg holes. The posterior condylar resection guide is impacted into position, and the osteotomy of the posterior condyle is made. The distal femur is then milled with use of a number-0 spigot, and the femoral component trial is positioned into place. The femoral condyle is "resurfaced" with the femoral component, which restores joint obliquity and the natural height, a critical element of the femur-first technique. Following this, the 1-mm (size-dependent) spherical gauge is placed around the femoral component trial. The tibial guide is secured with the G-clamp and a number-0 resection block, and is pinned into place. We recommend swapping the number-0 cutting guide for a +2 when making the cut in order to avoid over-resection. Recutting is advised if a minimum 3-mm feeler gauge does not adequately occupy the flexion space. The final step is to balance the flexion and extension gaps in the usual fashion. Alternatives: The alternative technique is a traditional tibia-first approach, in which tibial resection is performed prior to femoral resection. As described in the original manufacturer's manual, the tibial cut is accomplished with use of a number-0 cutting guide, and the tibial rotation is based on the axis formed by the anterior superior iliac spine and knee center, irrespective of the femoral condyle. Rationale: The femur-first technique is advantageous in several ways. When performing the femoral cut first, the surgeon can better align the drill guide at the center of medial femoral condyle. This will result in the femoral component being positioned more in line with the coronal plane of the femoral condyle. Additionally, the tibial resection is made with the femoral trial in place; therefore, the depth of resection can be more accurate, potentially avoiding excessive bone resection. Finally, with the femoral trial in place, the surgeon can judge the rotation and medial-lateral position of the tibial component more precisely, hence lowering the possibility of bearing spin-out, impingement, and dislocation or unexplained pain. Expected Outcomes: The femur-first technique is a bone-preserving procedure that results in thinner bearings when compared with a tibia-first approach1. The femur-first approach also improves radiographic outcomes, including femoral coronal, femoral sagittal, and tibial sagittal alignments, while tibial coronal alignment does not differ. There is an early trend toward improved 5-year survivorship with the femur-first (98%) versus tibia-first (94%, p = 0.35) techniques. There has been no significant difference reported in Knee Society Scores between techniques. Important Tips: Perform a preliminary cut of the posterior tibial cartilage in order to allow insertion of the femoral drill guide under the femoral condyle.Make sure the femoral drill guide lies in the center of the marked medial femoral condyle.Align the tibial sagittal cut with the femoral component trial in order to avoid bearing impingement.Be conservative in the tibial cutting by utilizing a +2 cutting guide (since the coupling is performed with the intramedullary guide in place, which drives the tibial guide distally). Acronyms and Abbreviations: UKA = unicompartmental knee arthroplastyFF = femur-firstM-L = medial-lateralAP = anteroposteriorPA = posteroanteriorASA = acetylsalicylic acid (aspirin)BID = bis in die, twice a dayPT = physical therapyTF = tibia-firstFCA = femoral coronal angleFSA = femoral sagittal angleTSA = tibial sagittal angleIM = intramedullaryOA = osteoarthritis.

Incidence, treatment, and outcomes of modern dual-mobility intraprosthetic dissociations.

Aims: Dual-mobility (DM) components are increasingly used to prevent and treat dislocation after total hip arthroplasty (THA). Intraprosthetic dissociation (IPD) is a rare complication of DM that is believed to have decreased with contemporary implants. This study aimed to report incidence, treatment, and outcomes of contemporary DM IPD. Methods: A total of 1,453 DM components were implanted at a single academic institution between January 2010 and December 2021: 695 in primary and 758 in revision THA. Of these, 49 presented with a dislocation of the large DM head and five presented with an IPD. At the time of closed reduction of the large DM dislocation, six additional IPDs occurred. The mean age was 64 years (SD 9.6), 54.5% were female (n = 6), and mean follow-up was 4.2 years (SD 1.8). Of the 11 IPDs, seven had a history of instability, five had abductor insufficiency, four had prior lumbar fusion, and two were conversions for failed fracture management. Results: The incidence of IPD was 0.76%. Of the 11 IPDs, ten were missed either at presentation or after attempted reduction. All ten patients with a missed IPD were discharged with a presumed reduction. The mean time from IPD to surgical treatment was three weeks (0 to 23). One patient died after IPD prior to revision. Of the ten remaining hips with IPD, the DM head was exchanged in two, four underwent acetabular revision with DM exchange, and four were revised to a constrained liner. Of these, five (50%) underwent reoperation at a mean 1.8 years (SD 0.73), including one additional acetabular revision. No patients who underwent initial acetabular revision for IPD treatment required subsequent reoperation. Conclusion: The overall rate of IPD was low at 0.76%. It is essential to identify an IPD on radiographs as the majority were missed at presentation or after iatrogenic dissociation. Surgeons should consider acetabular revision for IPD to allow conversion to a larger DM head, and take care to remove impinging structures that may increase the risk of subsequent failure.

Femoral Coronal Malalignment is Associated With Failure in Mobile-Bearing Medial Unicompartmental Knee Arthroplasty.

BACKGROUND: Femur-first (FF) technique for mobile-bearing medial unicompartmental knee arthroplasty (UKA) has been described as an alternative to tibia-first (TF) technique. The aim of this study was to compare the radiographic results in UKAs using FF or TF techniques and their influence on failure rates. METHODS: We retrospectively reviewed 288 UKAs with a minimum 2-year follow-up. There were 147 knees in the TF and 141 knees in the FF cohorts. Alignment parameters and overhang were assessed as outliers and far outliers. The mean follow-up was 6 years (range, 2 to 16), the mean age was 63 years (range, 27 to 92), and 45% of patients were women. Univariate and multivariate statistical analyses were carried out with Cox regression models. RESULTS: There were 13 and 6 revisions in the TF and FF cohorts, respectively. The FF had lower rates of femoral coronal alignment (FCA) or femoral sagittal alignment outliers compared to the TF (5.7% versus 19%, P = .011). Tibial coronal alignment and tibial sagittal alignment did not significantly differ between the techniques (22.7% in FF versus 29.9% in TF, P = .119). Overhang outliers did not differ significantly between the groups. Younger age was associated with a higher revision rate (P = .006), while FF versus TF, sex, body mass index, and postoperative mechanical axis did not show statistically significant associations. In multivariate analysis, FCA outliers and younger age were significantly associated with revision. CONCLUSIONS: The FF technique in mobile-bearing UKA resulted in fewer FCA outliers compared to TF. Despite improved knee alignment with the FF technique, FCA outliers and younger age were associated with a higher revision rate, independent of technique.

The Frank Stinchfield Award: Assembly and Dissociation Forces Differ Between Commonly Used Dual Mobility Implants: A Biomechanical Study.

BACKGROUND: Intraprosthetic dissociation (IPD) is a complication unique to dual mobility (DM) implants where the outer polyethylene head dissociates from the inner femoral head. Increasing reports of IPD at the time of closed reduction of large head DM dislocations prompted this biomechanical study evaluating the assembly and dissociation forces of DM heads. METHODS: We tested 17 polyethylene DM heads from 5 vendors. Of the heads, 12 were highly cross-linked polyethylene (4 vendors) and 5 were infused with vitamin E (2 vendors). Heads were between 46 and 47 mm in diameter, accepting a 28 mm-inner ceramic head. Implants were assembled and disassembled using a servohydraulic machine that recorded the forces and torques applied during testing. Dissociation was tested via both axial pull-out and lever-out techniques, where lever-out simulated stem-on-acetabular component impingement. RESULTS: The initial maximum assembly force was significantly different between all vendors (P < .01) and decreased for all implants with subsequent assembly. Vendor 4-E (Link with vitamin E) heads required the highest assembly force (1,831.9 ± 81.95 N), followed by Vendor 3 (Smith & Nephew), Vendor 5 (DePuy Synthes), Vendor 1-E (Zimmer Biomet with vitamin E), Vendor 2 (Stryker), and Vendor 1 (Zimmer Biomet Arcom). Vendor 4-E implants showed the greatest dissociation resistance in both pull-out (2,059.89 N, n = 1) and lever-out (38.95 ± 2.79 Nm) tests. Vendor 1-E implants with vitamin E required higher assembly force, dissociation force, and energy than Vendor 1 heads without vitamin E. CONCLUSIONS: There were notable differences in DM assembly and dissociation forces between implants. Diminishing force was required for assembly with each additional trial across vendors. Vendor 4-E DM heads required the highest assembly and dissociation forces. Vitamin E appeared to increase the assembly and dissociation forces. Based on these results, DM polyethylene heads should not be reimplanted after dissociation, and there may be a role for establishing a minimum dissociation energy standard to minimize IPD risk.