To our knowledge in medial unicompartmental knee arthroplasty (UKA) no study has specifically assessed the difference in outcome between matched gender groups. Previous unmatched gender studies have indicated more favourable results for women.

The use of arthroplasty registers was initiated by Sweden in 1979. The practice has been adopted globally as best practice for recording the outcome of joint replacement surgery and for identifying early problems. The Trent and Wales Arthroplasty Audit Group began in 1990 and have recently produced outcome results. We have analysed the short-term outcomes of arthroplasty procedures at a DGH in order to assess comparability to this “gold-standard”. In 2004, 231 primary arthroplasties were performed, by the two senior authors, at Musgrove Park Hospital (149 THR, 82 TKR). There was an overall complication rate of 8.7%. There was 1 periprosthetic infection in a THR that required revision (0.043%). 9 patients developed wound complications, principally superficial infections and haematoma formation. 2 patients, both THR developed, thromboembolic complications, one DVT and one pulmonary embolus. There was one periprosthetic fracture around a THR. The dislocation rate for THR was 3.35% (5/149). 3 of these were performed through a posterior approach and 2 through an anterolateral. 3 have required revision surgery. We have demonstrated comparable results following joint arthroplasty to published teaching hospital series. We have shown that adequate infrastructure can exist in smaller units to accurately record outcome data following arthroplasty surgery

Surgical results following proximal row carpectomy modified with proximal capitate resection and dorsal capsule interposition are presented. A consecutive cohort of thirteen patients was operated upon, and outcomes measured by radiograph, physical examination and DASH questionnaire. AROM values of 50° to 105° for the flexion/extension arc, restoration of grip strength to 72% of the contralateral extremity, and an improved functional outcome can be expected; and patients’ perceptions of functional outcome, as measured by the DASH, are significantly improved as early as six weeks. The results of PRC with interposition for stages II and III SLAC wrist were uniformly favorable.

Eaton has described two modifications to the proximal row carpectomy (PRC) procedure: partial capitate resection and dorsal capsular interpositional arthroplasty. The objective is to enlarge the radiocarpal interface to form a broad mobile pseudoarthrosis that would disperse compressive forces across the wrist more effectively. We present the first consecutive cohort of patients (n=13) who have undergone this procedure,

We extend the indications for PRC in this series to include those wrists with stage III SLAC deformity; approximately 67% of wrists had capitolunate arthritis.

AROM values of 50° to 105° for the flexion/extension arc, restoration of grip strength to 72% of the contralateral extremity, and an improved functional outcome can be expected from PRC with dorsal capsular interpositional arthroplasty.

Mean flexion/extension arc achieved was 86° (range, 50° to 105°). Radial deviation averaged 13° (range, 10° to 20°), and ulnar deviation averaged 21° (range, 15° to 25°). Grip strength averaged 72% of the contralateral extremity. The mean decline in the revised carpal height ratio was 24%. The mean DASH score was 20.8 (range, 10 to 29). Visual analog pain improved from 9.25 to 2.67 on average, with one patient reporting no pain with heavy exertion.

Patients were evaluated by active range of motion ; grip and pinch strength; radiographs; subjective analog pain; and DASH questionnaire.

Aims. The metabolic equivalent of task (MET) score examines patient performance in relation to energy expenditure before and after knee arthroplasty. This study assesses its use in a knee arthroplasty population in comparison with the widely used Oxford Knee Score (OKS) and EuroQol five-dimension index (EQ-5D), which are reported to be limited by ceiling effects. Methods. A total of 116 patients with OKS, EQ-5D, and MET scores before, and at least six months following, unilateral primary knee arthroplasty were identified from a database. Procedures were performed by a single surgeon between 2014 and 2019 consecutively. Scores were analyzed for normality, skewness, kurtosis, and the presence of ceiling/floor effects. Concurrent validity between the MET score, OKS, and EQ-5D was assessed using Spearman’s rank. Results. Postoperatively the OKS and EQ-5D demonstrated negative skews in distribution, with high kurtosis at six months and one year. The OKS demonstrated a ceiling effect at one year (15.7%) postoperatively. The EQ-5D demonstrated a ceiling effect at six months (30.2%) and one year (39.8%) postoperatively. The MET score did not demonstrate a skewed distribution or ceiling effect either at six months or one year postoperatively. Weak-moderate correlations were noted between the MET score and conventional scores at six months and one year postoperatively. Conclusion. In contrast to the OKS and EQ-5D, the MET score was normally distributed postoperatively with no ceiling effect. It is worth consideration as an arthroplasty outcome measure, particularly for patients with high expectations. Cite this article: Bone Jt Open 2023;4(3):129–137

Unicompartmental knee arthroplasty (UKA) is associated with a higher risk of revision compared with total knee arthroplasty (TKA). The outcomes of knee arthroplasty are typically presented as implant survival or incidence of revision after a set number of years, which can be difficult for patients and clinicians to conceptualise. We aimed to calculate the ‘lifetime risk’ of revision for UKA as a more relatable estimate of risk projection over a patient's remaining lifetime, and make comparisons to TKA. All primary UKAS performed from 1999 to 2019 (n=13,481) captured by the New Zealand Joint Registry (NZJR) were included. The lifetime risk of revision was calculated and stratified by age, gender and American Society of Anesthesiologists (ASA) status. The lifetime risk of revision for UKA was highest in the youngest patients (46-50 years; 40.4%) and lowest in the oldest patients (86-90 years; 3.7%). Lifetime risk of revision was higher for females (range 4.3%-43.4% cf. males 2.9%-37.4%) and patients with higher ASA status (ASA 3-4 range 8.8%-41.2% cf. ASA 1 1.8%-29.8%), regardless of age. The lifetime risk of UKA was two-fold higher than TKA (ranging from 3.7%-40.4% UKA, 1.6%-22.4% TKA) across all age groups. Increased risk of revision in the younger patients was associated with aseptic loosening in both males and females, and pain in females. Periprosthetic joint infections (PJI) accounted for 4% of all UKA revisions, in contrast to 27% for TKA; risk of PJI was higher for males than females for both procedures. The lifetime risk of revision is a more meaningful measure of arthroplasty outcomes and can aid with patient counselling prior to UKA. Findings from this study show the increased lifetime risk of UKA revision for younger patients, females and those with higher ASA status

Source of the study: University of Auckland, Auckland, New Zealand and University of Otago, Christchurch, New Zealand. Outcomes following knee arthroplasty are typically defined as implant survivorship at defined timepoints, or revision incidence over time. These estimates are difficult to conceptualise, and lack context for younger patients with more remaining years of life. We therefore aimed to determine a ‘lifetime’ risk of revision as a more useful metric for total (TKA) and unicompartmental knee arthroplasty (UKA). The New Zealand Joint Registry was used to identify 96,497 primary TKAs and 13,481 primary UKAs performed between 1999 and 2019. Patient mortality and revision incidence were also extracted. Estimates of lifetime risk were calculated using an actuarial lifetable method. The estimates were stratified by age and gender. Reasons for revision were categorised using previously published standardised definitions. The lifetime risk of UKA revision was two-fold higher than TKA across all age groups (range 3.7-40.4% UKA, 1.6-22.4% TKA). Revision risk was higher for males with TKA (range 3.4%-25.2% males, 1.1%-20% females), but higher for females with UKA (range 4.3%-43.4% vs. 2.9%-37.4% for males). Revision due to infections were higher for TKA (1.5% males, 0.7% females) compared with UKA (0.4% males, 0.1% females). The increased risk in younger UKA patients was associated with higher incidence of aseptic loosening (UKA 2%, TKA 1%) and ‘unexplained pain’ (UKA 2%, TKA 0.2%). The risk for UKA was two-fold higher than TKA, and this was partially explained by a higher proportion of revisions due to ‘unexplained pain’. For TKA, males had higher risk of revision, in contrast to UKA where females had higher risk; this gender difference was associated with higher incidence of infections with TKA. Younger age, gender and higher ASA status were also associated with increased lifetime risk of UKA revision. Lifetime risk of revision can provide a meaningful measure of arthroplasty outcomes to aid patient counselling

Aim. The current recommendation in Norway is to use four doses of a first-generation cephalosporin (cefazolin or cephalotin) as systemic antibiotic prophylaxis (SAP) the day of surgery in primary joint arthroplasty. Due to shortage of supply, scientific development, changed courses of treatment and improved antibiotic stewardship, this recommendation has been disputed. We therefore wanted to assess if one dose of SAP was non-inferior to four doses in preventing periprosthetic joint infection (PJI) in primary joint arthroplasty. Method. We included patients with primary hip- and knee arthroplasties from the Norwegian Arthroplasty Register and the Norwegian Hip Fracture Register for the period 2005-2023. We included the most used SAPs (cephalotin, cefazolin, cefuroxime, cloxacillin and clindamycin), administered as the only SAP in 1-4 doses, starting preoperatively. Risk of revision (Hazard rate ratio; HRR) for PJI was estimated by Cox regression analyses with adjustment for sex, age, ASA class, duration of surgery, reason for- and type of arthroplasty, and year of primary arthroplasty. The outcome was 1-year reoperation or revision for PJI. Non-inferiority margins were calculated for 1, 2 and 3 doses versus reference of 4 doses of SAP at the day of surgery, against a predetermined limit of 15% increased risk of PJI. Results. In total 274,188 primary arthroplasties (total hip 133,985, hemi hip 51,442, and total knee 88,761) were included. Of these primary arthroplasties, 2,996 (1.1%) had subsequent revisions for PJI during the first postoperative year. One dose of SAP was given in 9,603 arthroplasties, two doses in 10,068, three doses in 18,351, and four doses in 236,166 arthroplasties. With the recommended four doses as reference, the HRR (95% CI) for 1-year revision for infection was 0.9 (0.7-1.1) for one dose, 1.0 (0.8-1.2) for two doses, and 0.9 (0.8-1.1) for three doses. The corresponding adjusted 1-year revision incidences for PJI was 0.9 (0.7-1.1), 1.0 (0.8-1.2), 0.9 (0. 8-1.1) and 1.0 (1.0-1.1) for one, two, three and four doses respectively, and less than four doses was found to be non-inferior. Conclusions. One preoperative dose of SAP in primary joint arthroplasty surgery seems to be non-inferior to the current recommendation of four doses of a first-generation cephalosporin as PJI-prophylaxis. This finding may simplify the course of treatment for arthroplasty patients, save costs, and improve antibiotic stewardship

Aims

This study aims to evaluate the impact of metabolic syndrome in the setting of obesity on in-hospital outcomes and resource use after total joint replacement (TJR).

Aims

The primary aim was to assess whether preoperative health-related quality of life (HRQoL) was associated with postoperative mortality following total hip arthroplasty (THA) and knee arthroplasty (KA). Secondary aims were to assess whether patient demographics/comorbidities and/or joint-specific function were associated with postoperative mortality.

Aims

Our primary aim was to assess reoperation-free survival at one year after the index injury in patients aged ≥ 75 years treated with internal fixation (IF) or arthroplasty for undisplaced femoral neck fractures (uFNFs). Secondary outcomes were reoperations and mortality analyzed separately.

Background. Total knee arthroplasty (TKA) is a proven and cost-effective treatment for osteoarthritis. Despite the good to excellent long-term results, some patients remain dissatisfied. Our study aimed at establishing a predictive model to aid patient selection and decision-making in TKA. Methods. Using data from our prospective arthroplasty outcome database, 113 patients were included. Pre- and postoperatively, the patients completed 107 questions in 5 questionnaires: KOOS, OKS, PCS, EQ-5D and KSS. First, outcome parameters were compared between the satisfied and dissatisfied group. Secondly, we developed a new prediction tool using regression analysis. Each outcome score was analysed with simple regression. Subsequently, the predictive weight of individual questions was evaluated applying multiple linear regression. Finally, 10 questions were retained to construct a new prediction tool. Results. Overall satisfaction rate in this study was found to be 88%. We identified a significant difference between the satisfied and dissatisfied group when looking at the preoperative questionnaires. Dissatisfied patients had more preoperative symptoms (such as stiffness), less pain and a lower QOL. They were more likely to ruminate and had a lower preoperative KSS satisfaction score. The developed prediction tool consists of 10 simple, but robust questions. Sensitivity was 97% with a positive predictive value of 93%. Conclusions. Based upon preoperative parameters, we were able to partially predict satisfaction and dissatisfaction after TKA. After further validation this new prediction tool for patient satisfaction following TKA may allow surgeons and patients to evaluate the risks and benefits of surgery on an individual basis and help in patient selection

The December 2013 Knee Roundup. 360 . looks at: Conflict of interest and hyaluronic acid; Will time indeed tell in microfracture?; Contralateral knee pain and joint replacement outcomes; Patient satisfaction and knee replacement?; Hope in the cytokines for painful TKRs?; Pain severity, cytokines and osteoarthritis?; Quadriceps weakness and pain; and spontaneous osteonecrosis of the knee

Aims

While preoperative bloodwork is routinely ordered, its value in determining which patients are at risk of postoperative readmission following total knee arthroplasty (TKA) and total hip arthroplasty (THA) is unclear. The objective of this study was to determine which routinely ordered preoperative blood markers have the strongest association with acute hospital readmission for patients undergoing elective TKA and THA.

Besides eliminating pain, restoring activity is a major goal in orthopaedic interventions including joint replacement or trauma surgery following falls in frail elderly, both treatments of highest socio-economic impact. In joint replacement and even more so in frail elderly at risk of falling, turns are assessed in clinical tests such as the TUG (Timed Get-up-and-Go), Tinetti, or SPPB so that classifying turning movements in the free field with wearable activity monitors promises clinically valuable objective diagnostic or outcome parameters. It is the aim of this study to validate a computationally simple turn detection algorithm for a leg-worn activity monitor comprising 3D gyroscopes. A previously developed and validated activity classification algorithm for thigh-worn accelerometers was extended by adding a turn detection algorithm to its decision tree structure and using the 3D gyroscope of a new 9-axis IMU (56×40×15mm, 25g, f=50Hz,). Based on published principles (El-Gohary et al. Sensors 2014), the turn detection algorithm filters the x-axis (thigh) for noise and walking (Butterworth low-pass, 2. nd. order with a cut-off at 4Hz and 4. th. order with a cut-off at 0.3Hz) before using a rotational speed threshold of 15deg/s to identify a turn and taking the bi-lateral zero-crossings as start and stop markers to integrate the turning angle. For validation, a test subject wore an activity monitor on both thighs and performed a total of 57 turns of various types (walking, on-the-spot, fast/slow), ranges (45 to 360deg) and directions (left/right) in free order while being video-taped. An independent observer annotated the video so that the algorithmic counts could be compared to n=114 turns. Video-observation was compared to the algorithmic classification in a confusion matrix and the detection accuracy (true positives) was calculated. In addition, 4-day continuous activity measures from 4 test subjects (2 healthy, 2 frail elderly) were compared. Overall, only 5/114 turns were undetected producing a 96% detection accuracy. No false positives were classified. However, when detection accuracy was calculated for turning angle intervals (45°: 30–67.5°; 90°: 67.5–135°; 180°: 135–270°; 360°: 270–450°), accuracy for all interval classifications combined dropped to 83.3% with equal values for left and right turns. For the 180° and 360°, accuracy was 100% while for the shorter 45° and 90° turns accuracy was 75% and 71% only, mainly because subsequent turns were not separated. Healthy subjects performed between 470 (office worker) and 823 (house wife) turns/day while frail elderly scored 128 (high fall risk) to 487 turns/day (low fall risk). Turns/day and steps/day were not correlated. In healthy subjects ca. 50% of turns were in the 45° category compared to only ca. 35% in frail elderly. Turn detection for a thigh-worn IMU activity monitor using a computationally simple algorithm is feasible with high general detection accuracy. The classification and separation of subsequent short turns can be further improved. In multi-day measurement, turns/day and the distribution of short and long turns seem to be a largely independent activity parameter compared to step counts and may improve objective assessment of fall risk or arthroplasty outcome

The histopathology of periprosthetic tissues has been important to understanding the relationship between wear debris and arthroplasty outcome. In a landmark 1977paper, Willert and Semlitsch (1) used a semiquantitative rating to show that tissue reactions largely reflected the extent of particulate debris. Notably, small amounts of debris, including metal, could be eliminated without “overstraining the tissues” but excess debris led to deleterious changes. Currently, a plethora of terms is used to describe tissues from metal-on-metal (M-M) hips and corroded modular connections. We reviewed the evaluation and reporting of local tissue reactions over time, and asked if a dose response has been found between metal and tissue features, and how the use of more standardized terms and quantitative methodologies could reduce the current confusion in terminology. Methods. The PubMed database was searchedbetween 2000 and 2015 for papers using “metal sensitivity /allergy /hypersensitivity, Adverse Local Tissue Reaction (ALTR): osteolysis, metallosis, lymphocytic infiltration, Aseptic Lymphocytic Vasculitis-Associated Lesions (ALVAL), Adverse Reaction to Metal Debris (ARMD) or pseudotumor/ pseudotumour” as well as metal-on-metal / metal-metal AND hip arthroplasty/replacement. Reports lacking soft tissue histological analysis were excluded. Results. 131 articles describing M-M tissue histology were found. In earlier studies, the terms metal sensitivity / hypersensitivity /allergy implied or stated the potential for a Type IV delayed type hypersensitivity response as a reason for revision. More recently those terms have largely been replaced by broader terms such as ALTR, ALVAL and ARMD. ALVAL and metal hypersensitivity were often used interchangeably, both as failure modes and histological findings. Several histology scoring systems have been published but were only used in a limited number of studies. Correlations of histological features with metal levels or component wear were inconclusive, typically because of a high degree of variability. Interestingly, there were very few descriptions that concluded that the observed reactions were benign / normal or anticipated i.e. regardless of the histological features, extent of debris or failure mode, the histology was interpreted as showing an adverse reaction. Discussion. There is now an expanded set of terms to describe tissues but they lack clear definitions and typically do not use quantitative histological data to describe a wide range of periprosthetic reactions to metal. Lower limits of inflammation, necrosis or re-organization that represent a “normal” reaction to surgery and/or small amounts of wear debris are not clearly defined and are rarely discussed. The widespread adoption of the term “adverse” in the present tissue lexicon implies a cause and effect relationship between metal wear and corrosion products and histological features even though this has yet to be determined. The use of quantitative histological scores rather than subjective histological descriptions is imperative to improve the understanding and reporting of the range of periprosthetic reactions. In particular, a new lexicon that allows for a level of tissue reaction that is not misinterpreted as adverse is required

In the early days of total hip arthroplasty, the discussion of surgical approaches centered on issues related to obtaining optimum exposure for accurate insertion and fixation of implants and appropriate restoration of hip kinematics. More recently, attention has been directed to those aspects of exposure that appear to be associated with rapid recovery, shorter lengths of stay, less pain and minimal gait disturbance. The role of less invasive (“MIS”) exposures in achieving these outcomes has been sharply and extensively debated. Currently, the Direct Anterior Approach is being used by an increasing number of surgeons to address these outcomes. The purpose of this presentation is to discuss the relationship of total hip surgical approaches to peri-operative morbidity, rate of functional recovery, length of hospital stay and ultimate lower extremity function. Many factors affect the quality and rate of recovery from THA surgery. These include: 1) patient characteristics; 2) implant type; 3) surgical exposure and technique; and 4) peri-operative management. Numerous reports suggest that patient selection and effective peri-operative management have the greatest impact on the rate of recovery. The quality of the arthroplasty outcome is related to the accuracy with which the procedure is performed, regardless of the surgical approach used. Available evidence strongly suggests that the quality of the surgical technique used to perform a THA is a much more important determinant of outcome than the surgical approach used

Flexion contracture in total knee arthroplasty (TKA) remains a challenge. Soft tissue management and additional bone resection are traditional options for flexion contracture correction. Our hypothesis was that the post implant computer aided measurements would not be significantly different to the extension angles measured at six weeks post-operatively in the follow-up clinic. One hundred continuous TKA were performed by a single consultant using the OrthoPilot. ®. (BBraun, Aesculap) navigation system and Columbus implants. Of the group, 45 were male and 55 were female. Average age was 68 (range 49–87), mean BMI was 32.86 (22.26–51.86) and mean Oxford score preoperatively was 42 (range 21–56) and post-operatively 28 (range15–50). Data recorded at the preoperative assessment clinic included clinical flexion contracture and Oxford scores. Intra-operatively data were recorded using the navigation system. These included pre-operative flexion and extension angles, actual bone cuts of tibia and femur (both medial and lateral), postoperative correction of flexion and extension angles and soft tissue releases. At six weeks post operation, patients were seen in the follow clinic and clinical flexion contracture and Oxford score reassessed by the Arthroplasty outcome service. Measurements were grouped and comparisons were made using a Pearson Chi-square test. There was no relationship between post-implant extension angle measurements (by computer) and extension angles at six weeks (by goniometer) (p=0.682). Also, there was no relationship between pre-operative measurement angles collected at the pre-assessment (by goniometer) and the pre-implant angles measured on the table (by computer) (p=0.682). We found that BMI (up to 35) and postoperative Oxford scores were significantly related to the extension levels with values of (p=0.008) and (p=0.027) respectively. Pre-operative Oxford scores, pre-operative extension, amount of bony resection and soft-tissue releases did not show any significant relationship with the post-operative extension obtained at six weeks. The conclusions that we draw from this study are that there might be other factors that are likely to influence extension lag between the operation and the follow-up at six weeks. One of the factors that we could identify was the BMI. Attention to extensor lag is important because it leads to a poorer knee function, as indicated by the Oxford scores. Despite most of the post-implant measurement angles showing no extensor lag, about 20% of our patients still had more than five degrees flexion contracture at six weeks

Introduction This is a prospective, consecutive series of 178 prosthetic implantations to analyse single level versus multiple level cervical arthroplasty with two years minimum follow-up. Methods Fifty-five patients underwent a total of fifty-five Porous Coated Motion (PCM) cervical arthroplasties from C3–4 to C7–T1 (Group S for single level). Fifty-four patients underwent one hundred and nine multilevel PCM cervical arthroplasties (Group M for multilevel) during the same time interval, for the same indications, performed by the same surgeons under the same clinical protocol— double level, 43 cases; three levels, 7 cases: and four levels, 4 cases. Sixteen PCM cases had been performed as complex revision procedures with prior fusions—9 in Group S and 7 in Group M. They included 1 previous Bryan Disc, 1 cage-plate, 1 patient with Klippel-Feil disease, 3 patients had failed lordotic cervical cages. One additional patient in Group M had a fracture-dislocation at C4–5 with a pseudarthrosis at C3–4 and C5–6. The demographics between Group S and Group M were very similar—mean age of patients, gender, severity of neurologic symptoms and distribution of radicular and myeloradicular symptoms. Results There were no deaths, no infections, and no instances of iatrogenic neurologic progression in either the single level or the multiple level arthroplasty group. The mean EBL, length of surgery, and length of hospital stay were greater for the Multilevel Group. In contrast to these three operative demographic statistics, the self assessment outcomes instruments consistently showed more improvement for the multilevel cases. The mean improvement in the NDI for the single cases was 54.8 % (+/− 20.9) versus the multilevel cases mean improvement in NDI was 64.8 % (+/− 33.7). The mean improvement in the VAS showed the same relationship—single level mean improvement 62.0 % (26.9) versus the multilevel cases mean VAS improvement was 68.1% (+/− 31.4). The SF-36, Odoms, and TIGT were also more improved for the multilevel versus the single level group. The reoperation rates, adverse events, and incidence of complications were the same between the single level to the multilevel arthroplasty groups. Discussion This prospective report of cervical arthroplasty demonstrates that each cervical vertebral level is biomechanically independent of the adjacent level, whether it contains an arthoplasty or an unoperated intervertebral disc. With the Porous Coated Motion cervical arthroplasty the incidence of reoperation did not increase proportionately higher as the number of cervical levels requiring instrumentation increased. Even in three and four level arthroplasty the true benefits of cervical disk replacement outcomes were demonstrated on functional clinical outcomes at minimum two-year follow-up

Introduction. Our primary hypothesis was simple: does gait on a downhill gradient distinguish between types of knee arthroplasty? Our secondary hypotheses were these: are stride length and other kinematic variables affected by cruciate ligament integrity following knee arthroplasty?. Participants. Ethical approval was sought and gained prior to commencement of the study. 52 subjects were tested on the instrumented treadmill, 3 groups (UKA, TKA, and young healthy control) of 19, 14, and 19 respectively. The two high performing arthroplasty groups were recruited from a database of patient related outcome measures (PROMs) and were chosen based on high Oxford knee scores (OKS) with a minimum 12 months post hip arthroplasty. Gait Analysis. Gait performance was tested on a validated instrumented treadmill (Kistler Gaitway®, Kistler Instrument Corporation, Amherst NY)[22, 23]. The rear of the treadmill was ramped with 30 cm axle stands in order to create a 7 degree decline for downhill walking (figure 1). The speed was increased incrementally. Hof scaling and body weight normalising was also applied to the outputted mechanical data to correct for leg length and mass differences, respectively. Results. Patient Related Outcome Measures. Both arthroplasty groups outcome scores were substantially better than the average reported by national joint registries. Treadmill Gait Analysis. When walking fast downhill, UKA patients walked 15% faster than the TKA patients (1.75 vs 1.52 m/sec p=0.000) despite having the same cadence (134 vs 135step/min) (figures 2,3,4). The 15% difference in speed was largely due to the reduced mean step (p=0.001) and stride lengths (p=0.000) seen in the TKA patients. These finding persisted after Hof scaling, which normalised speed for leg length (p=0.000). The values are indicated as means ± standard deviation; †significant difference between implant versus control (p <0.05); ‡significant difference between implant groups (p<0.05);H=normalized to leg length; BW=normalized to body weight. Discussion. The UKA group walked 15% faster than the TKA, with stride length almost matching the normal controls. The presence of intact cruciate ligaments allow a normal and co-ordinated swing phase, enabling the more normal stride, while the absence of the anterior cruciate ligament contributes to the reduction of knee flexion in swing phase, and thus the shorter stride length