Published 11/1/2018

Second Look – Clinical

Hip and knee

Cost of THA—Total hip arthroplasty (THA) may be more cost-effective than nonoperative management (NM) regardless of patients’ body mass index (BMI), according to a long-term study published in The Journal of Arthroplasty (online). Researchers used a state-transition Markov model that included direct medical costs—but not indirect societal costs—to compare the THA and NM cohorts among six BMI groups in patients > 15 years old. The two highest BMI groups had higher incremental costs and quality-adjusted life years (QALY), but THA was still considered cost-effective among those cohorts. The incremental cost-effectiveness ratios (ICERs) for the six BMI groups were:

  1. normal weight (BMI, 18.5–24.9 kg/m2): $6,043/QALY
  2. overweight (25–29.9 kg/m2): $5,770/QALY
  3. obese (30–34.9 kg/m2): $5,425/QALY
  4. severely obese (35–39.9 kg/m2): $7,382/QALY
  5. morbidly obese (40–49.9 kg/m2): $8,338/QALY
  6. super obese (≥ 50 kg/m2): $16,651/QALY

With an ICER threshold of $50,000/QALY, the researchers found that THA was more cost-effective than NM in 100 percent of normal weight, overweight, obese, severely obese, and morbidly obese simulations, as well as 99.95 percent of super obese simulations. They theorized that BMI cutoffs for THA may contribute to unnecessary loss of healthcare access.

TKA PROMs—A study published in The Journal of Arthroplasty (September) found a correlation between kinematic factors and postoperative patient-reported outcome measures (PROMs) in total knee arthroplasty (TKA) patients. Researchers simulated deep knee bend kinematics for 96 postoperative TKA patients and measured the Knee Injury and Osteoarthritis Outcome Score (KOOS) 12 months postoperatively. They observed significant nonlinear relationships between the scores and rollback and dynamic coronal alignments. The “kinematic safe zone” was determined to be coronal angular change from extension to full flexion between zero and 4 degrees varus and measured rollback
≤ 6 mm without rollforward. The postoperative KOOS score was 10.5 points higher.

Falls after TKA—Patients undergoing TKA for osteoarthritis may be at risk for falls even after surgery, according to a systematic literature review published in the Journal of Orthopaedics (September). Researchers assessed 11 papers that included 1,237 patients for prevalence, risk factors, correlations with clinical outcomes, and effects of treatments of falls. Preoperative fall rates ranged from 23 percent to 63 percent, whereas postoperative fall rates ranged from 12 percent to 38 percent. Researchers found that clinical scales, BMI, and limited preoperative range of motion did not influence results. There was no indication that surgical or rehabilitative strategies reduced fall risk. Data on fall risk related to sex, fall history, age, kyphosis, muscle weakness, fear of falling, depression, balance, and gait impairment were conflicting.

PJI-related revision risks—A study published in The Lancet Infectious Diseases (online) found that modifiable and nonmodifiable factors may play a role in prosthetic joint infection (PJI) in total hip replacement patients. The prospective, observational cohort study included 2,705 primary hip procedures that were revised due to PJI between 2003 and 2014. The following were associated with an increased need for PJI-related revision: male sex, younger age
(< 60 years old), elevated BMI (≥ 30 kg/m2), diabetes, dementia, previous septic arthritis, fractured neck of femur, and use of the lateral surgical approach. Use of ceramic rather than metal bearings was associated with a decreased risk of
revision. Researchers noted that most factors had time-specific effects. The grade of the operating surgeon, absence of a consultant surgeon during surgery, and volume of procedures performed by the hospital had little to no impact on PJI risk.

Knee stiffness after tibial plateau fixation—The greatest risk factors for knee stiffness surgery in tibial plateau fixation patients appear to be the number of weeks spent in an external fixator and the presence of bilateral tibial plateau fracture, according to a study published in the Journal of Orthopaedic Trauma (September). The retrospective, observational cohort study compared 110 patients who underwent surgery (manipulation while under anesthesia, arthroscopic lysis of adhesion, or quadricepsplasty) for knee stiffness and 319 patients with tibial plateau fractures treated with open reduction and internal fixation who did not undergo surgery for knee stiffness (control group). The researchers found that external fixator time and bilateral tibial plateau fractures were significant predictors of surgical intervention for knee stiffness. They recommended that clinicians be aware of these risk factors as indicators of potential subsequent surgery.

Cementless unicompartmental knee replacement—A cohort study published in The Knee (online) found that cementless Oxford unicompartmental knee replacement (OUKR) may be a safe alternative to unicompartmental knee replacement with cement. Researchers measured clinical outcomes and survival among the first 1,000 consecutive cementless medial OUKRs implanted at one independent and one designer center. The 10-year survival rate was 97 percent, and only 25 knees required revision. The most common reason for revision was progression of arthritis laterally (n = 9), followed by primary dislocation of the bearing (n = 6). After a seven-year mean follow-up, the mean Oxford Knee Score improved from 23 to 42. Survivorship and clinical outcomes were not significantly different between the two centers.

THA in octogenarians—Uncemented THA appears to be a safe option for patients aged 80 years and older, according to a prospective cohort study published in The Journal of Arthroplasty (online). The study included 143 patients (mean age, 86.2 years) who underwent uncemented THA (n = 76) or hybrid THA (n = 67). The uncemented THA cohort had lower rates of intraoperative complication and transfusion. Mean hospital stays were similar: 11 days and 12 days for the cementless and hybrid THA cohorts, respectively. In each cohort, two patients required revision surgery. The researchers noted that age should not be a determining factor when choosing an implant; however, they recommended that surgeons use intraoperative assessment of bone quality to decide which implant is best.

Knee scooter flexion—Knee position with a scooter device may be linked to venous stasis, according to a study published in Foot & Ankle International (online). Thirteen healthy participants (mean age, 33 years) were included in the study. Researchers assessed comparative measurements while participants were standing and using the knee scooter. Standing versus using the scooter device was associated with a significant decrease in mean velocity (6.5 cm/s versus 3.2 cm/s) and volumetric flow rate (227.8 mL/min versus 106.2 mL/min). There were no significant differences associated with vessel diameter (0.82 cm versus 0.78 cm) or peak velocities (19.8 cm/s versus 14.7 cm/s). The researchers recommended that orthopaedists consider the risk attributed to the knee scooter as part of their overall patient assessment.

Knee implant orientation—A study published in The Journal of Arthroplasty (September) found that TKA position and orientation may impact polyethylene damage and how the knee performs postoperatively. Researchers compared three-dimensional CT measurements of prerevision TKA positioning with postrevision retrieval analysis for 30 TKA implants and calculated differences in thickness between medial and lateral components. Varus angulations were associated with thinner medial compartments, and valgus angulations were linked to thinner lateral compartments. Thickness varied among suboptimal tibial and tibiofemoral angulations.