Low Incidence of Postoperative Complications With Navigated Total Knee Arthroplasty.

BACKGROUND: A number of postoperative complications of navigated total knee arthroplasty (TKA) have been discussed in the literature, including tracker pin site infection and fracture. In this article, we discuss the low postoperative complication rate in a series of 3100 navigated TKAs and the overall complication rate in a systematic analysis of the literature. METHODS: Three thousand one hundred consecutive patients with navigated TKAs from 2001-2016 were retrospectively evaluated for complications specific to navigation. We discuss the 2 cases of postoperative fracture through tracker pin sites that we experienced and compare this systematically with the literature. RESULTS: Postoperatively, our 3100 patient cohort experienced a total of 2 fractures through pin sites for an incidence of 0.065%. One was a distal femoral fracture which was treated surgically, and the other was a proximal tibial fracture treated nonoperatively. Because of our incorporation of the tracker sites within our operative incision, there were no identifiable pin site infections, which others have noted at an incidence of 0.47%. Our 0.065% fracture rate compares favorably with the 0.16% rate of fracture published in the literature. CONCLUSION: There is an extremely low risk of perioperative complications because of the instrumentation used in navigated TKA when using the Stryker Navigation System and 4.0 mm anchoring pins placed within the surgical incision.

Medial over-resection of the tibia in total knee arthroplasty for varus deformity using computer navigation.

We are reporting a series of 35 cases in which downsizing, lateralizing of the tibial baseplate and resection of the uncovered medial plateau bone releases the medial collateral ligament and tightens the lateral collateral ligament. Result in excellent ligamentous balance and correction to neutral mechanical axis. The mean follow up was 32.8 months (11-95 months) and the average pre-operative varus was 9.47° (3.5-15°) with the average post-operative alignment was 0.65° varus. We obtained a mean correction of 0.45° for every mm (millimeter) of bone resected. We did not have any varus collapse or instability. Medial Over-resection could be employed as a technique in the management of varus OA knee with 2mm of resection giving about 10 correction of deformity.

Bone mineral density of the femur in autopsy retrieved total knee arthroplasties.

Bone mineral density (BMD), as measured by DEXA, can vary depending on bone rotation and fat content of soft tissues. We performed DEXA measurements, under controlled positioning, on 24 autopsy-retrieved femora from patients who had fully functional and asymptomatic successful TKA to determine periprosthetic BMD changes and compared results to 24 normal cadaveric femora. In TKA specimens, BMD was affected by gender, preoperative diagnosis, and zone under analysis. The lowest mean BMD was in the anterior femoral condylar zone. Males had higher mean BMD at all zones while patients with preoperative diagnosis of osteoarthritis had higher BMD in the posterior condylar zone. The mean BMD in the anterior femoral condylar zone in TKA specimens was significantly lower than in normal specimens without arthroplasties, most likely due to stress shielding.

Torsion deformity and joint loading for medial knee osteoarthritis.

PURPOSE: The consequences of lower limb torsion deformity on knee loading in knee osteoarthritis are poorly understood. The purpose of this study was to quantify the associations between the mechanical axis, tibial torsion and knee loading in subjects with medial knee OA and in controls. METHODS: Twenty-four subjects: end-staged medial knee osteoarthritis (OA) with apparent torsion deformity (TKO, n=6) and without torsion deformity (KOA, n=8) and controls (CON, n=10) were imaged using long standing lower extremity (LSLE) radiographs and computed tomography (CT). Medial knee loading was assessed using the internal knee varus moment determined by gait analysis. The LSLE mechanical axis, CT tibial torsion and the foot progression angle were used to predict medial knee loading. RESULTS: The TKOs had significantly greater mechanical axis varus and knee varus moment compared to KOAs and CONs. The regression model predicting medial knee loading using the mechanical axis (ß=0.898), tibial torsion (ß=0.264) and foot progression angle (ß=-0.369) showed a goodness of fit of 0.774. CONCLUSIONS: Medial knee loading was predicted by the mechanical axis and the foot progression angle. Future longitudinal studies are needed to assess the role of tibial intorsion during disease progression and following total knee replacement surgery.

Alignment in Total Knee Arthroplasty: Where Have We Come From and Where Are We Going?

Numerous reports have linked malaligned total knee arthroplasty (TKA) components with increased wear, poor functional outcomes, and possibly early failure due to component loosening. Consequently, proper alignment is critical to a successful outcome. This article will review: the normal mechanical alignment of the knee, classical alignment in TKA, anatomic alignment in TKA, intraoperative reference points for alignment, and the potential for new alignment schema based on the kinematic axes of knee movement. Along with our increased understanding of how the knee functions, modern total knee arthroplasty has evolved to restore a neutral mechanical axis when prostheses are implanted. Although historically the goal has been to aim to be within 3 degrees of this axis, recent reports have challenged the validity of the claim that outliers have an increased risk for revision. In addition, new alignment schemes have been developed based on the kinematic axes, but as yet we await verification of results to determine whether they increase the ability of total knee arthroplasty to provide a better-functioning and longer-lasting knee for the patient.

Soft-tissue balancing during total knee arthroplasty in the varus knee.

Soft-tissue balancing during total knee arthroplasty is an important step in optimizing the mechanical balance of the knee joint. Soft-tissue contractures that result from varus coronal plane deformity can pose a difficult problem, and the surgeon should have a standard procedure for managing such situations in the operating room. Balance may be assessed intraoperatively with the use of spacer blocks, laminar spreaders, and tensioning devices as well as by placement of trial components. Techniques used to balance the varus knee during primary total knee arthroplasty include femoral component rotation, osteophyte resection, soft-tissue release, and bone resection. Flexion and extension gap balancing is crucial for long-term success and patient satisfaction.

Using an antibiotic-impregnated cement rod-spacer in the treatment of infected total knee arthroplasty.

We present a new option for treatment of post-total knee arthroplasty periprosthetic infection associated with bone destruction and massive loss-use of an antibiotic-impregnated cement rod-spacer. This rod-spacer can be custom- made, at time of surgery, with Steinmann pins, intramedullary nails, Rush rods, Harrington spine rods, bone cement (polymethylmethacrylate), and antibiotics. We used this technique in 9 cases of periprosthetic infection over a 6-year period. The rod-spacer provided stable fixation across the knee, local antibiotic delivery, maintenance of the joint space, and preservation of soft-tissue tension around the joint through enhanced stability and length maintenance.

Resection arthroplasty for failed patellar components.

A total of 1,401 primary total knee arthroplasties (TKA) were reviewed; 44 (3.2%) had at least the patellar component revised. Nine of these knees (eight patients) had insufficient bone stock to allow reimplantation of another patellar component. Clinical data on the nine knees were obtained with recent follow-up evaluation, review of their medical records and radiographs. Evaluation included Hospital for Special Surgery (HSS) scores. Average follow-up was 4 years and 7 months, 2-year range (2 months to 8 years and 4 months). Common factors found in these nine knees included: thin patella after primary TKR status, osteoarthritis, good range of motion and patella alta. Results were good to excellent in seven knees and fair in two. The untoward associations with patellectomy such as quadriceps lag, extension weakness and anterior knee pain were not experienced. Resection of the patellar component, without reimplantation, is an acceptable alternative in revision TKA lacking adequate remaining bone stock.

The treatment of recurrent chronic infected knee arthroplasty with a 2-stage procedure.

We report the case of a patient with recurrent periprosthetic infections after total knee arthroplasty associated with bone destruction and massive bone loss that was successfully treated with a 2-stage procedure-resection arthroplasty with insertion of an antibiotic-impregnated cement rod-spacer and systemic antibiotics and then a resection arthrodesis of the knee with the use of an intercalary allograft fixed with a long intramedullary nail. This technique is a viable option for the treatment of recurrent periprosthetic infections after total knee arthroplasty associated with bone destruction, massive bone loss, and severe instability.

Surgical navigation in adult reconstruction surgery: techniques and clinical experience.

A surgeon's first response to the concept of computer-assisted orthopaedic surgery may be a sense of lost autonomy. However, a system need not and should not be designed to this end. Using the computational ability of the computer system to see beyond the human eye to view the knee with full kinematic dimensions, surgeons have recently made progress in the areas of computer-assisted ligament balancing and in using smart tools for minimally invasive surgery. Full comprehension of the use of any navigational system must begin with the understanding that the system can provide feedback that is based on only specifically programmed computer code. In referring to or locating a point or axis, the computer programmer must create an absolutely reliable methodology for determining that point or axis. Expecting the computer to achieve certain functionalities when physicians have no ironclad method to achieve such functionalities exposes the true limitations of any computer-assisted process. Although the computer generates a methodology, the process of computer-assisted surgery requires that the surgeon be constantly vigilant in analyzing the feasibility of these responses. Those instrumental in the development and implementation of computer-assisted surgical techniques must ensure that measurements are valid, precise, and reproducible across subjects and users. Prospective users of computer-assisted techniques must ensure that each of these issues has been addressed before agreeing to use the system in standard practice. Once due consideration has been given to all aspects of use, and the limitations of the system are known, the benefits of computer assistance are easily understood.

Passive knee kinematics before and after total knee arthroplasty: are we correcting pathologic motion?

The change in coronal plane deformity throughout a range of flexion before and after total knee arthroplasty (TKA) has not been reported. Unlike most alignment assessments traditionally reporting coronal plane alignment in a standing position under static conditions, this study reports deformity throughout the flexion arc before and after deformity correction. One hundred fifty-two TKA patients using the anteroposterior axis for femoral component rotation and computer navigation techniques were included in the study. Deformity before TKA ranged from 17.5 degrees varus (deformity apex away from the midline) to 20.5 degrees valgus (deformity apex toward the midline) in full extension. Before TKA, deformity was not constant through an arc of motion and significantly decreased with flexion of 60 degrees and more (P < .01). The deformity after performing a TKA was not different (P = .478) throughout the flexion arc. The data determined that deformity is not constant throughout flexion in osteoarthritic knees preoperatively and that deformity throughout flexion can be corrected with the use of conventional alignment techniques during TKA.

The effect of drill hole size on the fixation strength of a cemented prosthetic patellar button.

This study used a cadaver model to analyze the fixation strength of 3 different patellar resurfacing preparations using an all-polyethylene patellar component. One of 3 drill hole sizes was randomly selected and used to prepare the patella. The entire construct was cemented, mounted to a servohydraulic testing machine, cycled between 0 and 50 N, and then tested to failure. Mean forces obtained prior to failure were 258.5, 293, and 353.1 N for the chamfer, 4.5-mm, and 9.5-mm drill holes, respectively. There was a statistically significant difference in strength to failure between the 9.5-mm and chamfer drill hole sizes. These findings may help to reduce patellar implant failures.

Patellar meniscus in total knee arthroplasty.

Twenty-four clinically successful, autopsy retrieved porous-coated anatomic total knee arthroplasty (TKA) specimens were evaluated to determine the structure and function of the patellar meniscus. Mean implant duration was 76 months (range: 11-135 months). Histological examination showed the patellar meniscus to be composed of dense fibrous tissue with scattered regions of chronic granulomatous response to polyethylene debris. Patellar wear and polyethylene exposed patellar surface area were correlated with implant duration (r = 0.47, P = .03; r = 0.52, P = .06). Postoperative patellar tilt was also associated with patellar component wear (r = 0.64, P = .03). No other clinical measures were significantly associated with patellar wear or exposed surface area. Additional research is needed to determine what role, if any, the patellar meniscus plays in TKA outcomes.

Reliability of measuring long-standing lower extremity radiographs.

The mechanical axis of the lower extremity was measured using preoperative long-standing radiographs in 56 patients undergoing total knee arthroplasty with the Stryker Navigation System (Stryker, Kalamazoo, Mich). Each radiograph was measured by four physicians, three times, in random order, and at delayed intervals. Measurements from each physician produced intraclass correlation coefficients of 0.9872, 0.9973, 0.9958, and 0.9839. An intraclass correlation coefficient of 0.9844 was noted between each of the raters. Pre- and postoperative axial alignments were determined with Stryker Navigation. Preoperatively, each rater overestimated deformity approximately 1 degrees (P>.05); however, postoperatively each rater underestimated the degree of deformity by approximately 1 degrees (P>.05). Measuring long-standing lower extremity radiographs provides significant inter- and intrarater reliability in determining lower extremity alignment.

Pelvic tracker effects on hip center accuracy using imageless navigation.

OBJECTIVE: Imageless computer assisted total knee surgical systems have commonly relied on determination of the functional rotational center of the femoral head as a landmark for determining the lower extremity mechanical axis. This has been accomplished through range of motion and center of rotation calculations for the femur with respect to the pelvis as the lower extremity is taken through a range of motion. Our study evaluated the use of this algorithm with and without a pelvic tracker attached to the iliac crest. MATERIALS AND METHODS: The functional center of the hip joint was also compared to the true radiographic center as determined by spiral CT data. Evaluating the different methods on six lower extremities from three whole-body cadavers revealed significant differences in the location of the calculated hip joint center, but little difference in the resulting lower extremity mechanical axis determination. The functional hip joint centers measured with and without a pelvic tracker differed from one another and from the CT-determined hip center. RESULTS: No differences were found in the coronal plane measurements, but statistically significant differences were found in the sagittal plane measurements. CONCLUSION: Algorithms that reduce the noise generated by pelvic movement should be devised to eliminate the need for a pelvic tracker.

Effect of one- and two-pin reference anchoring systems on marker stability during total knee arthroplasty computer navigation.

OBJECTIVE: This study investigated different infrared marker reference base attachments in cadaveric bone and their effects on alignment outcome when different loads were applied. MATERIAL AND METHODS: Five cadaveric specimens were used to test four reference base attachments: a locking one-pin (4.0 mm and 5.0 mm pins) and a two-pin clamp (Hoffman fixator, 3.0 mm and 5.0 mm pins, Stryker Inc., NJ). Each was tested with metaphyseal and diaphyseal attachments. A navigation system (Stryker Navigation, MI) was used for testing with applied incremental loads and torques (65 N and 1.0 Nm) to the different reference base configurations. RESULTS: With 65 N the maximum change in distance to a verification point was 4.3 + 1.6 mm with the 4.0 mm locking pin in metaphyseal bone. No difference in verification point distances was found with any two-pin configuration. Alignment changes greater than 4 degrees resulted with the 65 N loads and a 4.0 mm pin. CONCLUSION: The results may prove beneficial in comparing the resulting error of different manufacturers and allow surgeons to realize the variability that may occur through incidental contact in the operating room.

Flexion and extension gap balancing in revision total knee arthroplasty.

UNLABELLED: Revision total knee arthroplasty presents a unique set of problems when attempting to balance flexion and extension gaps. Loss of soft tissue support and established deformity can make balancing difficult. One needs to balance the flexion and extension gap heights as well as medial and lateral symmetry, which may not always be attainable. We used a set of stepwise techniques to reestablish the joint line in extension using femoral augments, and then balanced the flexion gap using different sized femoral components. We retrospectively analyzed 45 patients who had revision total knee replacement with an average of 4 years followup. These patients had a mean flexion of 105 degrees and none had signs of instability in flexion or extension or on clinical exam. Despite the complex nature of revision knee arthroplasty, cases utilizing an algorithm to balance the extension and flexion gaps, with increased implant constraint when necessary, can aid in obtaining a good outcome. LEVEL OF EVIDENCE: Therapeutic study, level IV (case series). See Guidelines for Authors for a complete description of levels of evidence.

Extensor mechanism disruption after total knee arthroplasty.

UNLABELLED: Extensor mechanism disruption after total knee arthroplasty is a challenging complication for orthopaedic surgeons. The treatment options for repair include observation, direct primary repair, direct primary repair with synthetic ligament or autogenous tissue augmentation, or reconstruction with allograft tissue. A computerized systemic review and literature search was performed to identify the relevant literature on extensor mechanism disruptions associated with total knee arthroplasty. A comprehensive review of the literature and description of relevant treatment options and outcomes were performed using the information gained with the literature review. A multi-center prospective study on a consecutive series of patients recruited from the North American Knee Arthroplasty Revision (NAKAR) study was performed and data collected pre-operatively, intra-operatively, and post-operatively on patients that had a failed total knee arthroplasty using validated health related quality of life measures was analyzed. Six out of 290 patients in the study had extensor mechanism disruption and this group of patients had overall worse functional outcomes. The results of the study have solidified our knowledge that patients with extensor mechanism disruptions have worse functional outcomes and will need intensive management and rehabilitation. LEVEL OF EVIDENCE: Economic and decision analyses, level III (systematic review of level III studies). See Guide for Authors for a complete description of levels of evidence.

Differences between extramedullary, intramedullary, and computer-aided surgery tibial alignment techniques for total knee arthroplasty.

Traditionally, intramedullary and extramedullary tibial alignment techniques are used to obtain neutral alignment during total knee arthroplasty. Computer-assisted techniques are available to aid in obtaining alignment intraoperatively. This study analyzed the difference in tibial alignment using intramedullary and extramedullary techniques, and compared them to the resulting tibial axis as determined by a computer navigation system. The tibial alignment standard measure was determined by a spiral computed tomography (CT) study of each lower extremity. Intramedullary techniques resulted in a 1.3 degrees +/- 1.4 degrees of varus alignment and 4 degrees +/- 2.1 degrees increase in posterior slope while the extramedullary techniques resulted in 1.5 +/-1.8 degrees of valgus alignment and 1.8 degrees +/-1.1 degrees increase in posterior slope compared to the navigation system alignment. Direct measurement of metal markers on CT-scan analysis using the navigation system resulted in <0.5 degrees difference from the navigation data. Although the traditional alignment techniques are within a few degrees, the addition of the errors in all planes gives a much higher degree of error. Direct measurement of the mechanical axis using computer-guided surgical techniques for the tibia give a greater degree of accuracy compared to traditional alignment techniques.