[Functional outcomes and return to sports, work, and daily activities after revision UKA compared to primary UKA and TKA]. / Funktionelle Ergebnisse und Wiederaufnahme von Sport, Arbeit und Alltagsaktivitäten nach Revision eines Monoschlittens im Vergleich zur Primärimplantation eines Mono- und Doppelschlittens.

BACKGROUND: Unicompartmental knee arthroplasty (UKA), in addition to total knee arthroplasty (TKA), has been shown to be effective in the surgical treatment of knee osteoarthritis with appropriate patient selection. In clinical studies, it has demonstrated superior functional results with lower complication rates. In clinical practice, these advantages must be weighed against the disadvantage of an increased revision rate, especially in younger patients with sports and work activities. OBJECTIVES: The aim of this study was to compare the functional outcome as well as the time to return to daily activities, work, and sports after revision of UKA to TKA with those of primary UKA and primary TKA using a matched-pair analysis. MATERIALS AND METHODS: The study was based on a matched-pair analysis at two defined time points, always comparing 28 patients who underwent either revision of a UKA to a TKA, primary UKA, or primary TKA. Patients completed the Oxford Knee Score, UCLA score, Knee Society score, and WOMAC score during standardized follow-up. In addition, postoperative patient satisfaction and return to activities of daily living, work, and sports were recorded in a standardized manner, and a clinical examination was performed. RESULTS: The four functional scores studied showed a common trend in favor of UKA, followed by primary TKA and revision TKA. The differences between converted UKA and primary TKA were not significant. However, at 3.2 years after the last surgery, the results of the converted UKA were significantly lower than those of the primary UKA. Return to work and sports tended to occur the earliest after UKA, followed by TKA and the revision group. All groups showed a tendency to engage in low-impact sports. CONCLUSION: The functional results of revised UKA were significantly inferior to those of primary UKA based on a 3-year follow-up. Return to work, sports, and activities of daily living tended to take longer after revision than after primary implantation of either a UKA or a TKA.

Radiographic Evaluation of First Tarsometatarsal Joint Arthrodesis for Hallux Valgus Deformity: Does the Fusion of the First to the Second Metatarsal Base Reduce the Radiological Recurrence Rate?

BACKGROUND: Modified Lapidus arthrodesis (MLA) is a well-established treatment option for symptomatic hallux valgus deformity (HVD). However, recurrence of the deformity remains a concern. The goal of this study was to evaluate the effect of an additional intermetatarsal fusion on the radiographic recurrence rate after first tarsometatarsal (TMT-I) arthrodesis. METHODS: This is a retrospective evaluation of 56 feet that underwent TMT-I arthrodesis for moderate to severe HVD. Twenty-three feet received an isolated arthrodesis of the TMT-I joint (TMT-I), whereas 33 feet received an additional fusion between the base of the first and the second metatarsal bone (TMT-I/II). Various radiological parameters were determined preoperatively, 6 weeks and at a mean of 2 years postoperatively. RESULTS: The intermetatarsal angle (IMA) and the hallux valgus angle (HVA) were significantly lowered at both follow-up evaluations in both groups. In the TMT-I/II group, the initial reduction of HVA was significantly higher (29.3° vs 21.1°). This difference disappeared by the second follow-up, leaving no significant differences between both techniques at final follow-up. Radiological recurrence rates of HVD were comparable in both groups. CONCLUSIONS: Isolated TMT-I arthrodesis provides reliable radiological results in the correction of HVD. Whether additional fusion of the first and second metatarsal base should be routinely performed remains unclear. LEVELS OF EVIDENCE: Level 3.

Effect of bone density and cement morphology on biomechanical stability of tibial unicompartmental knee arthroplasty.

BACKGROUND: Unicompartmental knee arthroplasty (UKA) offers good long-term survivorship and superior kinematics and function compared with total knee arthroplasty (TKA). However, revision rates are higher with aseptic loosening representing a major cause. Biomechanical stability depends on cement penetration. The goal of this study was to analyze the influence of cement morphology and bone density on primary stability of tibial UKA under physiological loading conditions in human tibiae. METHODS: Thirty-six tibial trays were implanted in fresh-frozen human cadaver knees and tested for primary stability using dynamic compression-shear testing. Prior to implantation, bone density had been quantified for all 18 tibiae. Postoperatively, cement penetration has been assessed on frontal cuts based on eight predefined parameters. The influence of bone density and cement morphology on biomechanical stability was determined using correlation and linear regression analysis. RESULTS: Mean failure load was 2691 ± 832.9 N, mean total cement thickness was 2.04 ± 0.37 mm, mean cement penetration was 1.54 ± 0.33 mm and mean trabecular bone mineral density (BMD) was 107.1 ± 29.3 mg/ml. There was no significant correlation between failure load and cement morphology (P > .05). Failure load was significantly positive correlated with trabecular BMD (r = 0.843; P < .0001) and cortical BMD (r = 0.432; P = .0136). CONCLUSIONS: Simulating physiological loading conditions, the failure load of tibial UKA is linearly dependent on the trabecular BMD. The observed parameters of cementation morphology seem capable of preventing failure at the bone-cement interface before inherent bone stability is reached. Further research is required to assess the usefulness of a preoperative assessment of bone quality for patient selection in UKA.

A cone beam CT based 3D-assessment of bony forefoot geometry after modified Lapidus arthrodesis.

BACKGROUND: Modified Lapidus arthrodesis (MLA) is a well-established treatment modality for hallux valgus deformities (HVD) associated with instability of the first ray. Although the three-dimensional (3D) nature of HVD has long been recognized, diagnostics still focus on plain radiographs. The objective of this study was to validate 3D Cone Beam CT (CBCT) in the perioperative assessment of HVD with focus on the alignment of the forefoot. METHODS: In a prospective clinical study, MLA was performed on 30 patients (25 females, 5 males; mean age: 63.2 years). Pre- and postoperatively standard radiographs and CBCT with full weight-bearing were acquired. For the CBCT based assessment, reproducible criteria have been defined, measured, and correlated with established radiological indicators. RESULTS: Evaluation of standard radiographic parameters (hallux-valgus angle [HVA], intermetatarsal angle 1-2 [IMA 1-2], distal metatarsal articular angle [DMAA], tibial sesamoid position [TSP]) showed significant improvement postoperatively. Comparison of measurements obtained from plain radiographs and CBCT were significantly correlated between both measuring techniques, indicating high reliability. Pronation of the first metatarsal and the sesamoids were significantly reduced by the procedure. Due to this repositioning effect, the second metatarsal head was elevated by 3.1mm, and the lateral sesamoid was lowered by 3.8mm. However, there was no correlation between the amount of pronation and conventional radiographic measures. CONCLUSIONS: Compared to plain radiographs, CBCT allows a more detailed view of the forefoot alignment in the coronal plain after MLA. MLA was able to recenter the sesamoids under der first metatarsal head and conversely led to elevation of the second metatarsal head.

Impact of a double-layer cementing technique on the homogeneity of cementation and the generation of loose bone cement fragments in tibial unicompartmental knee arthroplasty.

BACKGROUND: The objective of this study was to evaluate the impact of a single- vs. double-layer cementing technique on morphological cementation and the generation of microscopic cement layers or loose cement fragments in unicompartmental knee arthroplasty (UKA). METHODS: UKAs were implanted in 12 cadaver knees. The specimens were divided into two groups of comparable bone mineral density. Six UKAs were implanted using a single-layer cementing technique (group A) and six UKAs were implanted using a double-layer cementing technique (group B). Morphological cementation was assessed on nine cuts through the implant-cement-bone interface in the frontal plane. Loose bone cement fragments and the microscopically quality of layer formation were evaluated. RESULTS: Contact between bone and prosthesis was observed in 45.4% of interfaces in group A and 27.8% in group B (p = 0.126). The significant increase of areas without visible cement interlocking in the anteroposterior direction in group A (p = 0.005) was not evident in group B (p = 0.262). Penetration around the peg tended to occur more frequently in group B (67.5% vs. 90.6% p = 0.091). Scanning electron microscopy identified no evidence of fissure formations within the bilaminar cement mantle. Free bone cement fragments were documented in 66.7% in both groups with no difference concerning mass (p = 1.0). CONCLUSIONS: This in-vitro study showed a tendency towards a more homogenous cementation of tibial UKAs using a double-layer cementing technique, although most of the differences did not reach the level of significance. However, theoretical downsides of the double-layer cementing technique such as an increased formation of free bone fragments or a microscopically fissure formation within the cement layer could not be detected either.

Influence of bone density on morphologic cement penetration in minimally invasive tibial unicompartmental knee arthroplasty: an in vitro cadaver study.

BACKGROUND: Unicompartmental knee arthroplasty is an established treatment option for anteromedial osteoarthritis. However, large registry studies report higher rates of aseptic loosening compared to total knee arthroplasty. The objective of this study was to assess the impact of bone density on morphological cement penetration. Moreover, an alternative regional bone density measuring technique was validated against the established bone mineral density assessment. METHODS: Components were implanted on the medial side of 18 fresh-frozen cadaver knees using a minimally invasive approach. Bone density has been quantified prior to implantation using Hounsfield units and bone mineral density. Morphological cement penetration has been assessed in different areas and was correlated with local bone density. FINDINGS: A highly significant correlation between Hounsfield units and trabecular bone mineral density was detected (r = 0.93; P < 0.0001), and local bone density was significantly increased in the anterior and posterior area (P = 0.0003). The mean cement penetration depth was 1.5 (SD 0.5 mm), and cement intrusion into trabecular bone was interrupted in 31.8% (SD 23.7%) of the bone-cement interface. Bone density was correlated significantly negative with penetration depth (r = - 0.31; P = 0.023) and positive with interruptions of horizontal interdigitating (r = + 0.33; P = 0.014). Cement penetration around the anchoring peg was not significantly correlated with bone density. INTERPRETATION: Areas with high bone density were characterized by significantly lower penetration depths and significantly higher areas without cement penetration. Anchoring pegs facilitate cement intrusion mechanically. Regional quantification of bone density using Hounsfield units is a simple but valuable extension to the established determination of bone mineral density.

Accuracy of a non-invasive CT-based measuring technique for cement penetration depth in human tibial UKA.

BACKGROUND: Aseptic loosening of the tibial component remains a major cause of failure in unicompartmental knee arthroplasty (UKA) and may be related to micro-motion at the cement-bone interface due to insufficient cement penetration depth. Cement penetration is therefore taken as an indicator of solid fixation strength and primary stability. However, its non-invasive clinical assessment remains difficult in vivo as conventional x-ray is prone to distortion and CT-scans (computed tomography) are difficult to assess due to metal artifacts. The purpose of this study was to develop and validate a reliable in vivo measuring technique of cement penetration depth in human tibial UKA. METHODS: In an experimental setting, twelve UKA were implanted in fresh-frozen human cadaver knees using a minimal-invasive medial approach. Cement penetration depth was then measured via 1) virtual 3D-models based on metal artifact reduced CT-scans and 2) histological evaluation of nine serial cross-section cuts through the implant-cement-bone-interface. Subsequently, a concordance analysis between the two measuring techniques was conducted. RESULTS: The average cement penetration depth was 1) 2.20 mm (SD 0.30 mm) measured on metal artifact reduced CT-scans and 2) 2.21 mm (SD = 0.42) measured on serial cuts (p = 0.956). The mean difference between both techniques was 0.01 mm (SD 0.31 mm) and the Person correlation coefficient was r = 0.686 (p = 0.014). All differences were within the upper and lower limit of agreement. There was no evidence of any significant proportional bias between both techniques (p = 0.182). CONCLUSIONS: CT-based non-invasive measurement of cement penetration depth delivers reliable results in measuring the penetration depth in tibial UKA. Thereby, it enables clinicians and researchers to assess the cement penetration for in vivo diagnostics in the clinical setting as well as in vitro biomechanical research with subsequent application of load to failure on the implant-cement-bone-interface.