Nathan G. Wetters

Leukocyte Esterase Reagent Strips for the Rapid Diagnosis of Periprosthetic Joint Infection

A total of 223 consecutive total hip or total knee arthroplasties were evaluated for periprosthetic joint infection (PJI) using leukocyte esterase reagent (LER) strips. Fifty-two LER strips were read as positive (23.3%), 106 were read as negative (47.5%), and 65 strips (29.2%) were unable to be read secondary to debris or blood in the aspiration. Using a synovial fluid white blood cell count of greater than 3000 white blood cell per microliter as an indicator of PJI, the sensitivity and specificity were 92.9% and 88.8%, respectively. When using positive cultures for diagnosis of PJI, sensitivity and specificity were 93.3% and 77.0% and 100% and 86.8% for the cases where a reoperation was performed and a combination of factors were used to define PJI. Leukocyte esterase reagent strips represent a rapid, inexpensive, and sensitive tool for the diagnosis of PJI. Their utility is limited, however, by blood or debris in the synovial fluid rendering them unreadable in one-third of cases.

Risk Factors for Periprosthetic Joint Infection Following Primary Total Hip Arthroplasty: A Case Control Study

The purpose of this study was to identify the specific comorbidities and demographic factors that are independently associated with an increased risk of periprosthetic joint infection (PJI) in total hip arthroplasty (THA) patients. A case-control study design was used to compare 88 patients who underwent unilateral primary THA and developed PJI with 499 unilateral primary THA patients who did not develop PJI. The impact of 18 comorbid conditions and other demographic factors on PJI was examined. Depression, obesity, cardiac arrhythmia, and male gender were found to be independently associated with an increased risk of PJI in THA patients. This information is important to consider when counseling patients on the risks associated with elective THA, and for risk-adjusting publicly reported THA outcomes.

Revision of unicompartmental arthroplasty to total knee arthroplasty: not always a slam dunk!

OBJECTIVE As the number of UKA performed in the world continues to increase, so will the number of failures. A better understanding of the outcomes after revision UKAto TKA is warranted. The objective of this study is to report the outcomes of modern UKA revised to TKA in three US centers. METHODS A total of 175 revisions of medial UKA in 168 patients (81 males, 87 females; average age of 66 years) performed from 1995 to 2009 in three institutions and with a minimum of 2-year clinical follow-up were reviewed. Individual joint registries and chart reviews were performed to collect data regarding reasons for revision, type of implants used, and re-revision rates. RESULTS The average time from UKA to revision TKA was 71.5 months (range 2 months to 262 months). The four most common reasons for failure of the UKA were femoral or tibial loosening (55%), progressive arthritis of the lateral or patellofemoral joints (34%), polyethylene failure (4%) and infection (3%). The average follow-up after revision was 75 months. Nine of 175 knees (4.5%) were subsequently revised at an average of 48 months (range 6 months to 123 months.) The rate of revision was 1.23 revisions per 100 observed component years. The average Knee Society pain and function score increased to 75 and 66, respectively. CONCLUSIONS In the present series, the re-revision rate after revision TKA from UKA was 4.5 % at an average of 75 months or 1.2 revisions per 100 observed component years. Compared to published individual institution and national registry data, re-revision of a failed UKA is equivalent to revision rates of primary TKA and substantially better than re-revision rates of revision TKA. These data should be used to counsel patients undergoing revision UKA to TKA.

Extensor mechanism allograft reconstruction for extensor mechanism failure following total knee arthroplasty.

BACKGROUND Extensor mechanism disruption following total knee arthroplasty is a rare but devastating complication. The purpose of this study was to report our experience with extensor mechanism allograft reconstruction for chronic extensor mechanism failure. METHODS Fifty consecutive extensor mechanism allograft reconstructions were performed in forty-seven patients with a mean age of 67.6 years who were followed for a mean time of 57.6 months (range, twenty-four to 125 months). The operative technique included the use of a fresh-frozen, correctly sized full extensor mechanism allograft that was tensioned tightly in full extension. Patients were evaluated clinically with use of the Knee Society score, and reconstructions were considered failures if the patient had a score of <60 points or a recurrent extensor lag of >30° or if they required revision or removal of the allograft. RESULTS Nineteen reconstructions (38%) were considered failures, including four revised to a second extensor mechanism allograft due to failure of the allograft, five for deep infection, and ten considered clinical failures secondary to a Knee Society score of <60 points or an extensor lag of >30°. The mean Knee Society score improved from 33.9 to 75.9 points (p<0.0001). The estimated Kaplan-Meier survivorship with failure for any reason as the end point was 56.2% (95% confidence interval, 39.4% to 70.1%) at ten years. CONCLUSIONS Extensor mechanism disruption following total knee arthroplasty is a difficult complication to treat, with modest outcomes. Extensor mechanism allograft reconstruction is a reasonable option; however, patients must be informed regarding the substantial risk of complications, and although initial extensor mechanism function may be restored, expectations regarding longer-term outcomes are more guarded.

Medial Unicompartmental Knee Arthroplasty in Patients Less Than 55 Years Old: Minimum of Two Years of Follow-Up

Eighty-five fixed bearing medial unicompartmental arthroplasties were performed in 42 men and 33 women with a mean age of 49 years (range, thirty-three to fifty-five years old) at the time of surgery. At a mean of 4.0 years (range two to twelve years), the mean pre-operative Knee Society score improved from 49 to 95.1 points (P<0.0001) and the mean UCLA activity score was 7.5 (range 5 to 9). Three knees underwent revision to a total knee arthroplasty; two for arthritic progression in the lateral compartment and one for pain. At the time of final follow-up, two knees (2.4%) demonstrated progressive Grade 4 arthritis of the patellofemoral compartment but were asymptomatic. There was no radiographic evidence of loosening, osteolysis, or premature polyethylene wear. Estimated survivorship was 96.5% at 10 years. UKA offered excellent early outcomes in this cohort of younger, active patients.

Should Draining Wounds and Sinuses Associated With Hip and Knee Arthroplasties Be Cultured

We assessed the utility of culturing draining wounds or sinuses in evaluating periprosthetic joint infection (PJI). Fifty-five patients with a draining wound or sinus after total joint arthroplasty (28 knees, 27 hips) who had not received antibiotics for at least two weeks were prospectively studied. Superficial wound cultures were compared to intra-articular cultures to determine accuracy in isolating infecting organism(s). The superficial cultures were concordant with deep cultures in 26 of 55 cases (47.3%) and were more likely to generate polymicrobial results (27.3% vs. 10.9%; P=0.023). In 23 cases (41.8%), the superficial cultures would have led to a change in antibiotic regimen. Superficial cultures yielded bacterial growth in 8 of the 10 cases (80%) when deep cultures and further work-up suggested the absence of deep infection. Given the potential to misguide diagnosis and treatment, we recommend against obtainment of superficial cultures in patients with a draining wound or sinus following hip or knee arthroplasty.

The use of abduction bracing for the prevention of early postoperative dislocation after revision total hip arthroplasty.

One potential strategy to decrease the risk of dislocation after revision total hip arthroplasty (THA) is the use of an abduction brace to limit flexion and adduction. The purpose of this study was to compare the dislocation rate after revision THA between patients treated with or without an abduction brace. Data were obtained from 1211 revision THAs performed in 610 women and 518 men who had a mean age of 64.7 years (range, 22-95 years) and were followed up for a minimum of 90 days. Five hundred two patients were braced, whereas 650 were not. The 90-day dislocation rate among patients who wore a brace was 5.2% compared with 5.7% in the nonbrace group (P = .70). Multivariate regression found no benefit to bracing (P = .37), while controlling for factors found to significantly affect dislocation rate in this population. Our data do not support the routine use of an abduction brace to aid in the prevention of dislocation.

Diagnosis of periprosthetic joint infection after unicompartmental knee arthroplasty

The purpose of this multicenter study is to determine the utility of the erythrocyte sedimentation rate, C-reactive protein, and synovial fluid white blood cell (WBC) count and differential for evaluating periprosthetic joint infection (PJI) in patients with a failed unicompartmental knee arthroplasty (UKA). A total of 259 patients undergoing revision of a failed UKA were reviewed; 28 (10.8%) met the study criteria for PJI. The optimal cutoff values were 27 mm/h for the erythrocyte sedimentation rate, 14 mg/L for the C-reactive protein, 6200/μL for the synovial fluid WBC count, and 60% for the differential. These tests are useful for diagnosing PJI after UKA with optimal cutoff values that are similar to those used for total knee arthroplasty; however, the optimal synovial WBC count was found to be somewhat higher, which may be related to the unresurfaced compartments. In addition, we found that nearly half of patients had suboptimal evaluation for PJI.

DeNovo NT Particulated Juvenile Cartilage Implant

Biological repair of focal chondral defects represents a significant clinical challenge as cartilage lacks intrinsic healing ability. Although it can be difficult to measure the objective success of cartilage repair techniques, the primary objective is symptom relief leading to less pain and improved function for the patient. Likely, the most important key to success is proper clinical indications. Second to this, the type of cartilage treatment utilized should be based on lesion location, size, depth, and other patient factors. One such treatment is DeNovo Natural Tissue. This method relies on the ability of juvenile chondrocytes to migrate from cartilage explants after being secured in a cartilage defect. Although approximately 8700 cases have been performed since 2007, long-term clinical outcomes are not yet available. However, basic science and early clinical data are promising.

Repair of Intraoperative Injury to the Medial Collateral Ligament During Primary Total Knee Arthroplasty

BACKGROUND Optimal treatment for intraoperative injury to the medial collateral ligament (MCL) during primary total knee arthroplasty remains controversial. While some advocate primary ligament repair and a period of bracing, others suggest conversion to a knee prosthesis with increased intrinsic constraint. The purpose of this study was to characterize the outcomes of primary repair followed by bracing. METHODS We performed a retrospective review of consecutive primary total knee arthroplasties to identify patients with intraoperative MCL laceration or avulsion treated with primary repair. Midsubstance lacerations were treated with end-to-end suture repair, whereas a screw-and-washer construct, suture, and/or suture anchors were used for reattachment of avulsions. All patients were instructed to wear an unlocked hinged knee brace for six weeks postoperatively. Patients were evaluated at a minimum of two years postoperatively for evidence of instability or other modes of failure and complications. RESULTS An intraoperative MCL injury occurred during forty-eight (1.2%) of the 3922 total knee arthroplasties that had been performed. One patient died less than two years postoperatively, one was lost to follow-up, and one underwent an intraoperative conversion to a constrained total knee arthroplasty, leaving forty-five total knee arthroplasties available for study. There were twenty-four midsubstance lacerations and twenty-one avulsions; thirty-five of these injuries occurred during a cruciate-retaining total knee arthroplasty and ten, during a posterior-stabilized total knee arthroplasty. At a mean of ninety-nine months (range, twenty-four to 214 months), there were no symptoms or physical examination findings of instability. The mean Hospital for Special Surgery knee score increased from 47 preoperatively to 85 at the time of follow-up (p < 0.001). Five knees required intervention for stiffness (four manipulations and one revision), and two required revision for aseptic loosening. CONCLUSIONS Our results suggest that intraoperative MCL injury can be treated with primary repair followed by hinged knee bracing without the need for increased prosthetic constraint. Stiffness, however, was a common complication.