Survivorship and clinical outcome of the minimally invasive Uniglide medial fixed bearing, all-polyethylene tibia, unicompartmental knee arthroplasty at a mean follow-up of 7.3years.

BACKGROUND: Medial UKA performed in England and Wales represents seven to 11% of all knee arthroplasty procedures, and is most commonly performed using mobile-bearing designs. Fixed bearing eliminates the risk of bearing dislocation, however some studies have shown higher revision rates for all-polyethylene tibial components compared to those that utilize metal-backed implants. The aim of the study is to analyse survivorship and maximum eight-year clinical outcome of medial fixed bearing, Uniglide unicompartmental knee arthroplasty performed using an all-polyethylene tibial component with a minimal invasive approach. METHODS: Between 2002 and 2009, 270 medial fixed UKAs were performed in our unit. Patients were reviewed pre-operatively, five and eight years post-operatively. Clinical and radiographic reviews were carried out. Patients' outcome scores (Oxford, WOMAC and American Knee Score) were documented in our database and analysed. RESULTS: Survival and clinical outcome data of 236 knees with a mean of 7.3years follow-up are reported. Every patient with less than 4.93years of follow-up underwent a revision. The patients' average age at the time of surgery was 69.5years. The American Knee Society Pain and Function scores, the Oxford Knee Score and the WOMAC score all improved significantly. The five-year survival rate was 94.1% with implant revision surgery as an end point. The estimated 10years of survival rate is 91.3%. Fourteen patients were revised before the five-year follow-up. CONCLUSION: Fixed bearing Uniglide UKA with an all-polyethylene tibial component is a valuable tool in the management of a medial compartment osteoarthritis, affording good short-term survivorship. Level of evidence IV.

Bedside end-tidal CO2 tension as a screening tool to exclude pulmonary embolism.

End tidal carbon dioxide tension (P(ET,CO(2))) is a surrogate for dead space ventilation which may be useful in the evaluation of pulmonary embolism (PE). We aimed to define the optimal P(ET,CO(2)) level to exclude PE in patients evaluated for possible thromboembolism. 298 patients were enrolled over 6 months at a single academic centre. P(ET,CO(2)) was measured within 24 h of contrast-enhanced helical computed tomography, lower extremity duplex or ventilation/perfusion scan. Performance characteristics were measured by comparing test results with clinical diagnosis of PE. PE was diagnosed in 39 (13%) patients. Mean P( ET,CO(2)) in healthy volunteers did not differ from P( ET,CO(2)) in patients without PE (36.3+/-2.8 versus 35.5+/-6.8 mmHg). P(ET,CO(2 )) in patients with PE was 30.5+/-5.5 mmHg (p<0.001 versus patients without PE). A P(ET,CO(2)) of >or=36 mmHg had optimal sensitivity and specificity (87.2 and 53.0%, respectively) with a negative predictive value of 96.6% (95% CI 92.3-98.5). This increased to 97.6% (95% CI 93.2-99.) when combined with Wells score <4. A P(ET,CO(2)) of >or=36 mmHg may reliably exclude PE. Accuracy is augmented by combination with Wells score. P( ET,CO(2)) should be prospectively compared to D-dimer in accuracy and simplicity to exclude PE.

Early failure of a mobile-bearing unicompartmental knee replacement.

Concerned by a perceived high revision rate, we retrospectively reviewed the survivorship of a series of 43 cemented, medial, mobile-bearing Preservation unicompartmental knee replacements implanted during a 2-year period at a single institution. The initial post-operative AP and lateral radiographs were independently assessed to test the hypothesis that suboptimal implantation of the prosthesis was responsible for early failure. An X-ray scoring system based on the criteria for assessing the Oxford mobile-bearing unicompartmental knee replacement was devised. The components of this score included assessment of prosthesis alignment, sizing and cementation. Nine (21%) LCS Preservation mobile-bearings prostheses had required revision at a mean of 22 months post-implantation. The commonest causes for failure were pain (44%) and tibial component loosening (33%). Analysis of post-operative radiographs showed no difference (n.s.) between the compound error scores for the revised and the surviving prostheses. No particular surgical error was identifiable leading to subsequent need for revision. The high failure rates shown in this study have led us to cease using this implant. The clinical relevance of this study is that the captive running track of the LCS mobile-bearing prosthesis may over constrain the meniscal component leading to early failure.

Does the joint line matter in revision total knee replacement?

We identified 148 patients who had undergone a revision total knee replacement using a single implant system between 1990 and 2000. Of these 18 patients had died, six had developed a peri-prosthetic fracture and ten had incomplete records or radiographs. This left 114 with prospectively-collected radiographs and Bristol knee scores available for study. The height of the joint line before and after revision total knee replacement was measured and classified as either restored to within 5 mm of the pre-operative height or elevated if it was positioned more than 5 mm above the pre-operative height. The joint line was elevated in 41 knees (36%) and restored in 73 (64%). Revision surgery significantly improved the mean Bristol knee score from 41.1 (SD 15.9) pre-operatively to 80.5 (SD 15) post-operatively (p < 0.001). At one year post-operatively both the total Bristol knee score and its functional component were significantly better in the restored group than in the elevated group (p < 0.01). Overall, revision from a unicondylar knee replacement required less use of bone graft, fewer component augments, restored the joint line more often and gave a significantly better total Bristol knee score (p < 0.02) and functional score (p < 0.01) than revision from total knee replacement. Our findings show that restoration of the joint line at revision total knee replacement gives a significantly better result than leaving it unrestored by more than 5 mm. We recommend the greater use of distal femoral augments to help to achieve this goal.

A comparison of patient based outcome following knee arthrodesis for failed total knee arthroplasty and revision knee arthroplasty.

Arthrodesis of the knee is an infrequently performed operation perceived by both patient and surgeon to have a poor outcome. This study compares functional outcome of knee arthrodesis following failed primary arthroplasty with that of revision knee arthroplasty in a matched patient group. Outcome was measured using the SF12 and Oxford Knee Score. Twelve patients underwent arthrodesis, of which eight were available for functional review at a mean of 53 months. No significant difference was found between the outcome scores of the two groups, although it is recognised that the numbers involved were low. Arthrodesis of the knee may be considered as a surgical option following failed arthroplasty when factors are present that may mitigate against an optimal result following revision knee arthroplasty.

The Avon patellofemoral arthroplasty: five-year survivorship and functional results.

We report the mid-term results of a new patellofemoral arthroplasty for established isolated patellofemoral arthritis. We have reviewed the experience of 109 consecutive patellofemoral resurfacing arthroplasties in 85 patients who were followed up for at least five years. The five-year survival rate, with revision as the endpoint, was 95.8% (95% confidence interval 91.8% to 99.8%). There were no cases of loosening of the prosthesis. At five years the median Bristol pain score improved from 15 of 40 points (interquartile range 5 to 20) pre-operatively, to 35 (interquartile range 20 to 40), the median Melbourne score from 10 of 30 points (interquartile range 6 to 15) to 25 (interquartile range 20 to 29), and the median Oxford score from 18 of 48 points (interquartile range 13 to 24) to 39 (interquartile range 24 to 45). Successful results, judged on a Bristol pain score of at least 20 at five years, occurred in 80% (66) of knees. The main complication was radiological progression of arthritis, which occurred in 25 patients (28%) and emphasises the importance of the careful selection of patients. These results give increased confidence in the use of patellofemoral arthroplasty.

Causes of failure of the Kinemax Plus total knee replacement in the first five years.

In order to investigate whether any single batch of polyethylene inserts was responsible for premature failure of total knee replacements (TKR), we performed a retrospective database review of 1133 consecutive primary Kinemax Plus TKR performed by 2 surgical teams between January 1992 and January 2001 at our institution. Cases re-operated in any way within 5 years of the index arthroplasty were identified, case notes studied and radiographs reviewed. The causes contributing to the premature failure of the implants were identified where possible and the polyethylene lot numbers were recorded. Nineteen cases were known to have been revised, 7 cases for deep infection of the prosthesis and 12 for aseptic failure. In 10 cases, an identifiable technical error had contributed to the early failure of the implant. In 4 of these cases, there was inadequate tissue balancing in patients with a significant pre-operative valgus deformity. In 2 cases, the tibial base plate was inserted in a varus mal-alignment. There was one extended tibial component, one internally rotated femoral component, one oversized femoral component and one femoral component with inadequate fixation. Two further cases failed aseptically, one with a fracture of the medial tibial plateau and one idiopathic. The lot numbers of the polyethylene inserts were all different. This study confirms that the premature failure rate of the Kinemax Plus TKR is low. Although a "bad batch" of polyethylene has been suggested as a cause for early failure in TKR, in this series, surgical error was the predominant cause.

Survivorship of the St Georg Sled medial unicompartmental knee replacement beyond ten years.

There have been several reports of good survivorship and excellent function at ten years with fixed-bearing unicompartmental knee replacement. However, little is known about survival beyond ten years. From the Bristol database of over 4000 knee replacements, we identified 203 St Georg Sled unicompartmental knee replacements (174 patients) which had already survived ten years. The mean age of the patients at surgery was 67.1 years (35.7 to 85) with 67 (38.5%) being under 65 years at the time of surgery. They were reviewed at a mean of 14.8 years (10 to 29.4) from surgery to determine survivorship and function. There were 99 knees followed up for 15 years, 21 for 20 years and four for 25 years. The remainder failed, were withdrawn, or the patient had died. In 58 patients (69 knees) the implant was in situ at the time of death. Revision was undertaken in 16 knees (7.9%) at a mean of 13 years (10.2 to 21.6) after operation. In seven knees (3.4%) this was for progression of arthritis, in three (1.5%) for wear of polyethylene, in four (2%) for tibial loosening, in two (1%) for fracture of the femoral component and in two (1%) for infection. Two knees (1%) were revised for more than one reason. The mean Bristol knee score of the surviving knees fell from 86 (34 to 100) to 79 (42 to 100) during the second decade. Survivorship to 20 years was 85.9% (95% CI 82.9% to 88.9%) and at 25 years was 80% (95% CI 70.2% to 89.8%). Satisfactory survival of a fixed-bearing unicompartmental knee replacement can be achieved into the second decade and beyond.

No deterioration of kinematics and cruciate function 10 years after medial unicompartmental arthroplasty.

The mechanisms of failure for unicompartmental arthroplasty are poorly understood. There is some suggestion that long term ligament degeneration, particularly of the anterior cruciate ligament (ACL), may affect long term survivorship. This study evaluated whether the cruciate mechanism remained functional in the long term (10 years) following UKA. Two separate cohorts of patients who had undergone St Georg Sled medial compartmental arthroplasty had knee kinematics assessed using an established fluoroscopic technique. One group (early) was assessed at a mean of 46 months (3.8 years) since surgery, whilst the other (late) was assessed at a mean of 125 months (10.4) following surgery. No significant difference was found in the sagittal plane kinematics between the two groups or in comparison to the control normal knee. The results suggest that after fixed bearing UKA the cruciate mechanism remains intact over time and the ligaments continue to function similarly to those of the normal knee.

The progression of arthritis following lateral unicompartmental knee replacement.

In order to aid patient selection we have analysed the radiological progression of arthritis in the retained compartments following lateral unicompartmental knee replacement (UKR). Patients undergoing lateral UKR (St Georg Sled, Waldemar Link) between 1988 and 1999 were assessed. Radiographs taken post-operatively within 8 weeks and at 5 years were assessed. OA was classified using both the Altman and Ahlbach scoring systems. Identifying information on each radiograph was obscured so that the observer was blinded. Each radiograph was reviewed twice to assess intra-observer variability. Patients were assessed clinically using the Bristol Knee Score (BKS) at 1 and 5 years post-operation. Reproducibility for the Ahlbach systems was shown to be very good (kappa = 0.86) and the Altman moderate (kappa = 0.41). Thirty-two lateral UKRs were assessed at 5 years. Six out of 32 of the knees assessed showed definite progression of OA on the Ahlbäch score in the retained medial compartment and 11 out of 32 on the Altman. There was a statistically significant increase in the grade of OA, as assessed by both systems, at 5 years as compared to the post-operative radiograph (p < 0.001). The definite progression group had a mean BKS 10 points lower at 5 years. Six patients required revision to TKR for progression of arthritis in the retained compartments. Lateral compartment UKR can be a very successful procedure, but there is a greater rate of progression of arthritis in the retained medial compartment than following medial UKR.

Arthritis progression after patellofemoral joint replacement.

Progressive symptomatic tibiofemoral osteoarthritis (OA) following patellofemoral joint replacement (PFJR) may necessitate revision to total knee arthroplasty. This study was designed to quantify this problem in a prospective series of 103 consecutive patients who underwent PFJRs undertaken at our institution. At a mean follow-up of 7.1 years (66-102 months), 14 knees (14%) have been revised, 12 of those (12%) because of the development of symptomatic tibiofemoral OA, with a mean time to revision of 55 months (range 14 to 95 months). Available radiographs of the 89 unrevised knees were subject to blinded and randomised assessment by two observers. Postoperative AP knee radiographs were scored to assess for tibiofemoral OA progression, with definite progression seen in a median of 7% of medial compartments but 0% of lateral compartments, over a mean period of 51 months. Sulcus angles on preoperative 30 degrees skyline radiographs were measured to assess for trochlear dysplasia. Seventeen percent of the knees without preoperative trochlear dysplasia have been revised for progression of tibiofemoral OA, compared to none of the knees with preoperative trochlear dysplasia. Furthermore, in the unrevised knees, statistically significantly more radiographic progression of tibiofemoral OA was seen in those without preoperative trochlear dysplasia (p = 0.01). Our results suggest that progressive tibiofemoral OA following PFJR is an important cause of failure, but it is seen significantly less frequently when the patellofemoral arthritis is secondary to dysplasia of the femoral trochlea, suggesting that these patients are the ideal candidates for PFJR.

Is anterior knee pain a predisposing factor to patellofemoral osteoarthritis?

Adolescent anterior knee pain has traditionally been described as running a benign and self-limiting course. Studies more recently have questioned this supposition. This study aimed to assess how many patients who had undergone patellofemoral arthroplasty for isolated patellofemoral arthritis had previously suffered from adolescent anterior knee pain, knee instability and trauma. This group was then compared to a control group of medial unicompartmental arthroplasty patients. Both groups were surveyed by postal questionnaire, with a >75% response rate from each group. 22% of the patellofemoral arthroplasty group described adolescent or early adulthood anterior knee pain as compared to 6% in the medial unicompartmental arthroplasty group (p<0.001). Patients in the patellofemoral group had also suffered significantly more patellofemoral instability and trauma than the medial unicompartmental group (p<0.001 and p=0.02, respectively). A significant number of patients with patellofemoral arthritis have described preceding anterior knee pain in their adolescence and early adult years, raising the question as to whether anterior knee pain may be one of the contributing factors to patellofemoral osteoarthritis in later years.

Customised hinged knee replacements as a salvage procedure for failed total knee arthroplasty.

BACKGROUND: Failure of knee arthroplasty can lead to significant pain and functional disability. In a small number of patients with fracture, sepsis or massive bone loss they are considered for arthrodesis or above knee amputation. The purpose of this study was to investigate the results and complications of using customised hinged knee replacements in their place. METHODS: Since 1993, 30 of the 280 (10.7%) revision knee replacements in the Avon Orthopaedic Centre, Bristol have used Endo customised hinged knee prostheses (21 rotating, nine fixed) for salvage of limb threatening situations in elderly patients. Surgical indications were 22 low periprosthetic fractures (with or without aseptic loosening), five massive aseptic osteolyses, and three deep infections. RESULTS: The mean length of post-operative hospital stay was just 14.6 days and all patients were discharged walking with aids. At follow up (mean 3.0 years, range 0.5-9.3 years) nine patients had died with their prostheses in situ and functioning. Six patients developed deep sepsis, two of which underwent above knee amputation, and two had received further surgery for septic problems. Two patients required further surgery for prosthetic disarticulation and one patient had successful on table vascular repair. Twenty-five patients had mid- or long- term follow up. Their mean American Knee scores (AKS) were 69.8 for knee and 35.6 for function (maximum 100), with mean total knee flexion 83 degrees. Mean Oxford knee scores (OKS) and WOMAC scores (both scored between 12 and 60 with low score indicating less difficulties) were 34.0 and 30.5, respectively. CONCLUSIONS: Customised hinge revision knee replacements gave rapid rehabilitation and hospital discharge. Complications were high but at mid- and long-term review, no prostheses had failed from an aseptic cause and most of the knees of this challenging group were providing both stability and flexion.

Fixed or mobile bearing unicompartmental knee replacement? A comparative cohort study.

Unicompartmental knee replacement (UKR) for anteromedial osteoarthritis is a well-established technique. Numerous clinical outcome studies demonstrate good medium and long-term results. The aim of this prospective study was to compare the complications and short-term clinical outcome of the St. Georg Sled, a fixed bearing UKR, with the Oxford mobile bearing UKR. Outcome at 2 years was assessed using the Bristol knee score and the Oxford knee score; in addition, complications occurring since formal scoring at 2-year follow-up were recorded. A total of 47 Oxford UKRs and 57 St. Georg Sled UKRs were performed in 91 patients, none of whom were lost to follow-up. At 2 years, both outcome measures were better for the St. Georg Sled Group. The pain component of the Bristol knee score was significantly better for this group (p-value = 0.013). Three patients in the Oxford group had bearing dislocations and a further four patients required revision (mean time to revision 3.0 years). In the St. Georg Sled group, three patients required revisions (mean time to revision 3.4 years). These results demonstrate that in the short-term, the Oxford mobile bearing prosthesis has a higher re-operation rate and that the St. Georg Sled achieves better pain relief. The functional scores of the two groups were similar.

Radiological changes ten years after St. Georg Sled unicompartmental knee replacement.

Failure of a unicompartmental knee replacement (UKR) may be caused by progressive osteoarthritis of the knee and/or failure of the prosthesis. We have examined the fate of the other compartments of the knee by radiological assessment 10 years after operation. A total of 50 UKRs were performed on 45 carefully selected patients between 1989 and 1992. Fifteen patients died, two patients were lost to follow-up and two knees were revised. Standard long-leg weight-bearing anteroposterior views of the knee and skyline views of the patellofemoral joint were taken pre-operatively and at 8 months and 10 years after operation. The radiographs of the remaining 30 knees were reviewed three times by blind and randomized assessment to measure the progression of osteoarthritis within the joints. Two knees showed evidence of progression of osteoarthritis within the patellofemoral joint and three knees showed some progression of the opposite tibiofemoral compartment--but only on one of the radiological grading systems used for assessment. It is concluded that progression of arthritis in the unreplaced compartments is not a significant problem after fixed bearing UKR.

Hidden blood loss following hip and knee arthroplasty. Correct management of blood loss should take hidden loss into account.

Following total hip arthroplasty (THA) and total knee arthroplasty (TKR) only the 'visible' measured blood loss is usually known. This underestimates the 'true' total loss, as some loss is 'hidden'. Correct management of blood loss should take hidden loss into account. We studied 101 THAs and 101 TKAs (with re-infusion of drained blood). Following THA, the mean total loss was 1510 ml and the hidden loss 471 ml (26%). Following TKA, the mean total loss was 1498 ml. The hidden loss was 765 ml (49%). Obesity made no difference with either operation. THA involves a small hidden loss, the total loss being 1.3 times that measured. However, following TKA, there may be substantial hidden blood loss due to bleeding into the tissues and residual blood in the joint. The true total loss can be determined by doubling the measured loss.

Polyethylene wear in a non-congruous unicompartmental knee replacement: a retrieval analysis.

Polyethylene wear is considered a threat to the long-term survival of unicompartmental knee replacement (UKR). This study aims to determine the linear penetration and volumetric wear associated with a non-congruent commonly used UKR, the St Georg Sled. This prosthesis has a biconvex femoral component which articulates with a flat polyethylene tibial component resulting in point contact. Components were retrieved from the knees of 19 patients undergoing revision for a failed UKR after primary replacement. Linear penetration and volumetric wear was measured using a coordinate measuring machine. Using an un-used implant, a three-dimensional computer model of the surface was generated and compared to the explanted specimen. Most patients had revisions because of disease progression to other compartments rather than specific wear related pathology. The mean linear wear for the sample was 0.89 mm (S.D. 0.59 mm) over an average period of 5.6 years giving the mean linear penetration rate of 0.15 mm/year. The mean volumetric wear was 99.7 mm3 (S.D. 79.3 mm3) over the same period giving a mean annual volumetric wear rate of 17.3 mm3/year. The results in this study indicate that clinically significant wear is not necessarily a feature of this fixed bearing unicompartmental knee replacement. The pattern of wear is consistent with clinical findings and indicates excavation of the polyethylene after implantation but at a slower rate than would be anticipated.

Trochlear resurfacing for extensor mechanism instability following patellectomy.

Patellectomy may in some cases result in persistent pain, weakness and instability of the knee. We report on three patients who had extensor tendon instability and were treated by trochlear resurfacing and extensor tendon realignment. All three cases achieved pain relief and an impressive improvement in knee function.