Denis Nam

Systematic Review of Patient-specific Instrumentation in Total Knee Arthroplasty: New but Not Improved

BackgroundPatient-specific cutting blocks have been touted as a more efficient and reliable means of achieving neutral mechanical alignment during TKA with the proposed downstream effect of improved clinical outcomes. However, it is not clear to what degree published studies support these assumptions.Questions/purposesWe asked: (1) Do patient-specific cutting blocks achieve neutral mechanical alignment more reliably during TKA when compared with conventional methods? (2) Does patient-specific instrumentation (PSI) provide financial benefit through improved surgical efficiency? (3) Does the use of patient-specific cutting blocks translate to improved clinical results after TKA when compared with conventional instrumentation?MethodsWe performed a systematic review in accordance with Cochrane guidelines of controlled studies (prospective and retrospective) in MEDLINE® and EMBASE® with respect to patient-specific cutting blocks and their effect on alignment, cost, operative time, clinical outcome scores, complications, and survivorship. Sixteen studies (Level I–III on the levels of evidence rubric) were identified and used in addressing the first question, 13 (Level I–III) for the second question, and two (Level III) for the third question. Qualitative assessment of the selected Level I studies was performed using the modified Jadad score; Level II and III studies were rated based on the Newcastle-Ottawa scoring system.ResultsThe majority of studies did not show an improvement in overall limb alignment when PSI was compared with standard instrumentation. Mixed results were seen across studies with regard to the prevalence of alignment outliers when PSI was compared with conventional cutting blocks with some studies demonstrating no difference, some showing an improvement with PSI, and a single study showing worse results with PSI. The studies demonstrated mixed results regarding the influence of PSI on operative times. Decreased operative times were not uniformly observed, and when noted, they were found to be of minimal clinical or financial significance. PSI did reliably reduce the number of instrument trays required for processing perioperatively. The accuracy of the preoperative plan, generated by the PSI manufacturers, was found lacking, often leading to multiple intraoperative changes, thereby disrupting the flow of the operation and negatively impacting efficiency. Limited data exist with regard to the effect of PSI on postoperative function, improvement in pain, and patient satisfaction. Neither of the two studies we identified provided strong evidence to support an advantage favoring the use of PSI. No identified studies addressed survivorship of components placed with PSI compared with those placed with standard instrumentation.ConclusionsPSI for TKA has not reliably demonstrated improvement of postoperative limb or component alignment when compared with standard instrumentation. Although decisive evidence exists to support that PSI requires fewer surgical trays, PSI has not clearly been shown to improve overall surgical efficiency or the cost-effectiveness of TKA. Mid- and long-term data regarding PSI’s effect on functional outcomes and component survivorship do not exist and short-term data are scarce. Limited available literature does not clearly support any improvement of postoperative pain, activity, function, or ROM when PSI is compared with traditional instrumentation.

Accelerometer-Based, Portable Navigation vs Imageless, Large-Console Computer-Assisted Navigation in Total Knee Arthroplasty: A Comparison of Radiographic Results

Computer-assisted surgery (CAS) systems improve alignment accuracy in total knee arthroplasty (TKA) but have not been widely implemented. Eighty knees underwent TKA using an accelerometer-based, portable navigation device (KneeAlign 2; OrthAlign Inc, Aliso Viejo, California), and the radiographic results were compared with 80 knees performed using a large-console, imageless CAS system (AchieveCAS; Smith and Nephew, Memphis, Tennessee). In the KneeAlign 2 cohort, 92.5% of patients had an alignment within 3° of a neutral mechanical axis (vs 86.3% with AchieveCAS, P < .01), 96.2% had a tibial component alignment within 2° of perpendicular to tibial mechanical axis (vs 97.5% with AchieveCAS, P = .8), and 94.9% had a femoral component alignment within 2° of perpendicular to the femoral mechanical axis (vs 92.5% with AchieveCAS, P < .01). The mean tourniquet time in the KneeAlign 2 cohort was 48.1 ± 10.2 minutes vs 54.1 ± 10.5 minutes in the AchieveCAS cohort (P < .01). Accelerometer-based, portable navigation is as accurate as large-console, imageless CAS systems in TKA.

Reverse total shoulder arthroplasty: Current concepts, results, and component wear analysis

After its introduction in the 1970s, reverse total shoulder arthroplasty had minimal clinical success, as its constrained design and lateralized glenohumeral center of rotation led to excessive shear forces and failure of the glenoid component1,2. Modern implant design modifications have emphasized a larger radius of curvature of the glenoid component and movement of the center of shoulder rotation medially and distally, creating a more stable and efficient fulcrum and decreasing shear forces at the glenoid-bone interface3,4. Since receiving U.S. Food and Drug Administration (FDA) approval in 2003, reverse total shoulder arthroplasty has become popular for use for more than rotator cuff-tear arthropathy; its uses include treatment of failed conventional total shoulder arthroplasties, rheumatoid arthritis in patients with an irreparable cuff tear, proximal humeral tumors, and proximal humeral fractures with anterosuperior escape5,6. However, with major complication rates as high as 26%7, limited implant longevity, and a lack of long-term functional outcome data, concerns have continued about its widespread use2. ### Source of Funding There was no external funding source for this investigation. Without injury, the glenohumeral joint possesses remarkable mobility and is able to remain stable over the majority of an individual’s life span. While both static and dynamic restraints contribute to its stability, the glenohumeral joint lacks substantial intrinsic osseous constraints8,9. Although the glenoid and the humeral head have similar shapes, they differ substantially in size. Warner demonstrated that the spherical humeral head has an articular surface area of approximately 21 to 22 cm2, while that of the glenoid is 8 to 9 cm2, with a maximum contact area of only 4 to 5 cm2 between the two surfaces10. This limited contact area and the shallow glenoid …

Observations on retrieved humeral polyethylene components from reverse total shoulder arthroplasty

HYPOTHESIS Analyses of polyethylene components retrieved at revision of total knee, hip, and shoulder replacements have been used to study the effect of design, patient, and surgical factors on initial implant performance, but no studies have reported similar types of findings in retrieved humeral polyethylene components in reverse total shoulder arthroplasty. Our hypothesis is that while the conforming surface of the humeral polyethylene may predispose it to surface wear modalities, as seen in total hip arthroplasty, the presence of clinical instability may also increase the occurrence of focal contact stresses leading to subsurface fatigue failure. MATERIALS AND METHODS Fourteen humeral polyethylene components were retrieved from revision surgery at a single institution. Each polyethylene was analyzed for 9 modes of damage in each of 4 quadrants into which the bearing surface was divided. For each implant, the most recent radiographs before removal were scored using an adapted radiolucency score, and glenosphere positioning was measured. RESULTS Despite the short mean length of implantation (0.46 ± 0.5 years), scratching and abrasion were seen in 14 and 13 components, respectively, followed by third-body debris and pitting. The modes of damage observed were most severe in the inferior quadrant of the humeral polyethylene. Scapular notching, glenoid, and humeral radiolucencies were prevalent on preoperative radiographs, but their long-term significance has not yet been elucidated. Increased glenosphere inclination was associated with decreased superior and total glenoid radiolucency, along with total polyethylene wear scores. DISCUSSION Promising early, functional results with the use of reverse total shoulder arthroplasty has led to the increased expansion of its use, but high complication and revision rates continue to raise concerns regarding implant longevity. The presence of a clinical, adduction deficit may predispose patients to inferior quadrant polyethylene wear. CONCLUSIONS Impingement of the humeral polyethylene at the lateral edge of the scapula leads to inferior quadrant wear and associated polyethylene failure, and implant instability may predispose the components to fatigue wear mechanisms. Analysis of retrieved humeral polyethylene components, along with patient, design, and surgical factors, provide important information on the causes of component failure.

Patient-Specific Instrumentation for Total Knee Arthroplasty: A Review

Patient-specific instrumentation is a new technology that offers increased surgical accuracy, which could decrease outliers, increased efficiency, involving fewer steps and shorter surgical times, and has the potential for cost-effectiveness, if overall surgical volume can be increased and future revision rates can be decreased. As with all technology, further studies are necessary, but there is much interest in this technology as medicine enters the age of increased patient burden and an increased emphasis on efficiency.

Ideal femoral head size in total hip arthroplasty balances stability and volumetric wear.

BackgroundOver the last several years, a trend towards increasing femoral head size in total hip arthroplasty to improve stability and impingement free range of motion has been observed.PurposeThe specific questions we sought to answer in our review were: (1) What are the potential advantages and disadvantages of metal-on-metal, ceramic-on-ceramic, and metal-on-polyethylene bearings? (2) What is effect that femoral head size has on joint kinematics? (3) What is the effect that large femoral heads have on bearing surface wear?MethodsA PubMed search and a review of 2012 Orthopaedic Research Society abstracts was performed and articles were chosen that directly answered components of the specific aims and that reported outcomes with contemporary implant designs or materials.ResultsA review of the literature suggests that increasing femoral head size decreases the risk of postoperative dislocation and improves impingement free range of motion; however, volumetric wear increases with large femoral heads on polyethylene and increases corrosion of the stem in large metal-on-metal modular total hip arthroplasty (THA); however, the risk of potentially developing osteolysis or adverse reactions to metal debris respectively is still unknown. Further, the effect of large femoral heads with ceramic-on-ceramic THA is unclear, due to limited availability and published data.ConclusionsSurgeons must balance the benefits of larger head size with the increased risk of volumetric wear when determining the appropriate head size for a given patient.

Extramedullary Guides Versus Portable, Accelerometer-Based Navigation for Tibial Alignment in Total Knee Arthroplasty: A Randomized, Controlled Trial: Winner of the 2013 HAP PAUL Award

Extramedullary (EM) tibial alignment guides have demonstrated a limited degree of accuracy in total knee arthroplasty (TKA). The purpose of this study was to compare the tibial component alignment obtained using a portable, accelerometer-based navigation device versus EM alignment guides. One hundred patients were enrolled in this prospective, randomized controlled study to receive a TKA using either the navigation device, or an EM guide. Standing AP hip-to-ankle and lateral knee-to-ankle radiographs were obtained at the first, postoperative visit. 95.7% of tibial components in the navigation cohort were within 2° of perpendicular to the tibial mechanical axis, versus 68.1% in the EM cohort (P<0.001). 95.0% of tibial components in the navigation cohort were within 2° of a 3° posterior slope, versus 72.1% in the EM cohort (P=0.007). A portable, accelerometer-based navigation device decreases outliers in tibial component alignment compared to conventional, EM alignment guides in TKA.

Rotator cuff tear arthropathy: evaluation, diagnosis, and treatment: AAOS exhibit selection.

Rotator cuff tear arthropathy encompasses a broad spectrum of pathology, but it involves at least three critical features: rotator cuff insufficiency, degenerative changes of the glenohumeral joint, and superior migration of the humeral head. Although many patients possess altered biomechanics of the glenohumeral joint secondary to rotator cuff pathology, not all patients develop rotator cuff tear arthropathy, and thus the exact etiology of rotator cuff tear arthropathy remains unclear. The objectives of this manuscript are to (1) review the biomechanical properties of the rotator cuff and the glenohumeral joint, (2) discuss the proposed causes of rotator cuff tear arthropathy, (3) provide a brief review of the historically used surgical options to treat rotator cuff tear arthropathy, and (4) present a treatment algorithm for rotator cuff tear arthropathy based on a patients clinical presentation, functional goals, and anatomic integrity.

Variability in the Relationship Between the Distal Femoral Mechanical and Anatomical Axes in Patients Undergoing Primary Total Knee Arthroplasty

Currently, an intramedullary (IM) guide is often used for performing the distal femoral resection in total knee arthroplasty (TKA). However, this method assumes that in most patients, the distal femoral mechanical-anatomical angle (FMAA) is 5°. Preoperative, standing, AP hip-to-ankle radiographs were reviewed in 493 patients undergoing primary TKA, and the FMAA was digitally measured. Correlation coefficients relative to several radiographic measurements, along with demographic variables, were performed. A significant number of patients (28.6%) had an FMAA outside the range of 5° ± 2° (range 2.0°-9.6°). The only measurement demonstrating a fair/moderate correlation with the FMAA was the neck-shaft angle (r = -0.55). Using an IM resection guide, without obtaining AP hip-to-ankle radiographs to determine each patients true FMAA, may lead to malalignment of the femoral component.

A rare case of a bisphosphonate-induced peri-prosthetic femoral fracture

An 81-year-old woman presented with a fracture in the left femur. She had well-fixed bilateral hip replacements and had received long-term bisphosphonate treatment. Prolonged bisphosphonate use has been recently linked with atypical subtrochanteric and diaphyseal femoral fractures. While the current definition of an atypical fracture of the femur excludes peri-prosthetic fractures, this case suggests that they do occur and should be considered in patients with severe osteopenia. Union of the fracture followed cessation of bisphosphonates and treatment with teriparatide. Thus, this case calls into question whether prophylactic intramedullary nailing is sufficient alone to treat early or completed atypical femoral fractures.