Björn Knutsson

Obesity Is Associated With Inferior Results After Surgery for Lumbar Spinal Stenosis : A Study of 2633 Patients from the Swedish Spine Register

Study Design. A cohort study based on the Swedish Spine Register. Objective. To determine the association between body mass index (BMI) and outcome of lumbar spine surgery for spinal stenosis. Summary of Background Data. Several small studies have sought to evaluate the importance of obesity in relation to results after surgery for lumbar spinal stenosis (LSS), but the findings are inconsistent and relatively weak. Methods. All patients who underwent surgery for LSS from January 1, 2006, to June 30, 2008, with a completed 2-year follow-up in the Swedish Spine Register were included. Logistic regression was used to assess the association between BMI and different outcomes. Results. Of the 2633 patients enrolled, 819 (31%) had normal weight, 1208 (46%) were overweight, and 606 (23%) were obese. On average, all 3 BMI groups achieved significant improvements after surgery. A higher BMI, however, was associated with greater odds of dissatisfaction after surgery and inferior results at the 2-year follow-up. After adjusting for differences in baseline characteristics, the obese group demonstrated inferior function and quality of life as measured by the Oswestry Disability Index (ODI) and the EuroQol Group Index (EQ-5D), respectively. At the 2-year follow-up, obese patients had a mean ODI of 33 (95% confidence interval [CI], 31–34) and mean EQ-5D of 0.56 (95% CI, 0.54–0.59) compared with a mean ODI of 25 (95% CI, 24–26) and mean EQ-5D of 0.64 (95% CI, 0.62–0.66) in the normal weight group. When compared with the normal weight patients, the adjusted odds ratio for dissatisfaction was 1.73 in the obese group (95% CI, 1.36–2.19). Differences between the normal weight and overweight groups were modest and therefore could not be considered clinically relevant. Conclusion. Obese patients achieved significant pain reduction, better walking ability, and improved quality of life after surgical treatment of LSS. Nevertheless, obesity was associated with a higher degree of dissatisfaction and poorer outcomes after surgery for LSS.

Adaptive end-to-end compression for variable-bandwidth communication

Abstract In this paper, we present a model for transport level compression with dynamic compression level adaptation, and we present an implementation of this model in Linux TCP, together with measurements showing what performance to expect when using adaptable end-to-end compression over wireless radio links and over an Ethernet. Measurements from our implementation show that for link speeds up to 10 Mbps, employing compression yields a throughput gain for most types of data. For slower speeds (e.g. 1–2 Mbps wireless radio links) this gain is significant (for the Calgary Compression Corpus files, the throughput increase is typically in the range of 50–200%, depending on link speed and data characteristics).

Body mass index and risk for clinical lumbar spinal stenosis : a cohort study

Study Design. A prospective cohort study that used a Swedish nationwide occupational surveillance program for construction workers (period of registration from 1971 to 1992). In all, 364,467 participants (mean age at baseline 34 yr) were included in the study. Objective. To determine whether overweight and obesity are associated with a higher risk of lumbar spinal stenosis (LSS). Summary of Background Data. During recent decades, LSS has become the most common indication for spine surgery, a change that coincides with a higher prevalence of obesity. Methods. A diagnosis of LSS was collected through individual linkage to the Swedish National Patient Register through December 31, 2011. Poisson regression models were employed to estimate multivariable-adjusted incidence rate ratios (IRRs) for LSS. Results. At baseline, 65% had normal weight (BMI [body mass index]: 18.5–24.99 kg/m2), 29% were overweight (BMI: 25–29.99 kg/m2), 5% were obese (BMI ≥30 kg/m2), and 2% were underweight (BMI <18.5 kg/m2). During 11,190,944 person-years of follow-up, with a mean of 31 years, 2381 participants were diagnosed with LSS. Compared with normal weight individuals, obese workers had an IRR of 2.18 (95% confidence interval, 1.87–2.53) for LSS and overweight workers had an IRR of 1.68 (95% confidence interval, 1.54–1.83). Workers who were underweight halved their risk of LSS (IRR: 0.52, 95% confidence interval, 0.30–0.90). Conclusion. Obese and overweight persons are at a higher risk of developing LSS. Furthermore, our results indicate that obesity might be a novel explanation for the increased number of patients with clinical LSS. Level of Evidence: 3

Substantially higher prevalence of postoperative periprosthetic fractures in octogenarians with hip fractures operated with a cemented, polished tapered stem rather than an anatomic stem: A prospective cohort study involving 979 hips

Background and purpose — Recent studies have demonstrated a high incidence of postoperative periprosthetic femoral fracture (PPF) in elderly patients treated with 2 commonly used cemented, polished tapered stems. We compared the prevalence and incidence rate of PPF in a consecutive cohort of octagenerians with femoral neck fractures (FNFs) treated with either a collarless, polished tapered (CPT) stem or an anatomic matte stem (Lubinus SP2). Patients and methods — In a multicenter, prospective cohort study, we included 979 hips in patients aged 80 years and above (72% females, median age 86 (80–102) years) with a femoral neck fracture as indication for surgery. 69% of the patients were classified as ASA class 3 or 4. Hip-related complications and repeat surgery were assessed at a median follow-up of 20 (0–24) months postoperatively. Results — 22 hips (2.2%) sustained a PPF at a median of 7 (0–22) months postoperatively; 14 (64%) were Vancouver B2 fractures. 7 of the 22 surgically treated fractures required revision surgery, mainly due to deep infection. The cumulative incidence of PPFs was 3.8% in the CPT group, as compared with 0.2% in the SP2 group (p < 0.001). The risk ratio (RR) was 16 (95% CI: 2–120) using the SP2 group as denominator. Interpretation — The CPT stem was associated with a higher risk of PPF than the SP2 stem. We suggest that the tapered CPT stem should not be used for the treatment of femoral neck fractures in patients over 80 years.

Obese patients report modest weight loss after surgery for lumbar spinal stenosis: a study from the Swedish spine register.

Study Design. SWESPINE, the Swedish Spine Register, was used for this cohort study. Objective. Our primary aim was to determine weight change in obese patients after surgery for lumbar spinal stenosis (LSS). Our secondary aim was to study any possible associations between weight loss after surgery and improvement in patient-related outcome measures (PROMs). Summary of Background Data. Only meager evidence is available as to how surgery for LSS affects weight and whether weight loss is associated with improvement in PROMs after surgery for LSS. Methods. All obese patients who underwent surgery for LSS from January 1, 2006 through June 30, 2008 with a completed 2-year follow-up in SWESPINE were included. Data for weight were collected before surgery and then 1 and 2 years after surgery. The cohort was divided into 3 subclasses (weight stable, weight loss, or weight gain). Results. Totally, 538 obese patients were enrolled. Mean weight loss was 1.9 kg (95% confidence interval, 1.5–2.3) 1 year after surgery and 2.0 kg (95% confidence interval, 1.5–2.4) after 2 years after surgery. Only 8% of the patients reported a clinically important weight loss (≥10%). No significant differences in PROMs were observed. The weight-stable group reported a mean improvement of 0.22 (standard deviation, 0.36) in EQ-5D, 14 (18) units in the Oswestry Disability Index, 18 (33) units in back pain (visual analogue scale), and 23 (36) units in leg pain (visual analogue scale). The corresponding changes in the weight-loss group were 0.23 (0.35) in EuroQol 5D, 15 (19) in Oswestry Disability Index, 27 (29) in back pain, and 31 (36) in leg pain. Conclusion. Modest weight loss was reported 1 and 2 years postsurgery; a small proportion (8%) of these patients reported a clinically important weight loss at the 2-year follow-up. The weight loss was unrelated to changes in PROMs. Level of Evidence: 3

Early periprosthetic joint infection and debridement, antibiotics and implant retention in arthroplasty for femoral neck fracture

Introduction Periprosthetic joint infection (PJI) is a severe complication of hip arthroplasty for femoral neck fractures (FNF). Debridement, antibiotics and implant retention (DAIR) is recommended in early PJI in association with stable implants. Few studies have evaluated the outcome of DAIR in this fragile population. The purpose of this study was to analyse risk factors for PJI and the short-term outcome of DAIR in FNF patients treated with a hip arthroplasty. Methods A consecutive series of 736 patients (median age 81 years, 490 women, 246 men) had been treated with either a total hip arthroplasty or a hemi hip arthroplasty for a displaced FNF at our institution. 33 (4.5%) of the hips developed an early (<6 weeks post operatively) PJI and 28 (3.8%) of these patients were treated according to the DAIR-protocol. Regression analyses were performed to assess risk factors for developing a PJI. Results DAIR eradicated the PJI in 82% (23/28) of patients at a median follow-up of 31 (SD 29.8) months of the infected hips. The logistic regression analysis indicated that 2 or more changes of the primary dressing due to wound bleeding was associated with an increased risk for developing PJI (OR 4.9, 95% 1.5 to 16.1, p = 0.01). Conclusions The short-term success-rate of DAIR was unexpectedly favourable in this fragile patient population; the results being on par with that after PJI in osteoarthritis patients. The need for repeated bandage changes postoperatively indicates an increased risk for PJI and should prompt early surgical intervention.

Substantially higher prevalence of postoperative periprosthetic fractures in octogenarians with hip fractures operated with a cemented, polished tapered stem rather than an anatomic stem: A prospective cohort study involving 979 hips: (Acta Orthop 2016; 87(3): 257-61)

Background and purpose - Recent studies have demonstrated a high incidence of postoperative periprosthetic femoral fracture (PPF) in elderly patients treated with 2 commonly used cemented, polished ...

Reduced revision rate and maintained function after hip arthroplasty for femoral neck fractures after transition from posterolateral to direct lateral approach

Background and purpose — The direct lateral (DL) approach to the hip for femoral neck fractures (FNF) has been shown to reduce the rate of dislocation and reoperations. We evaluate the effect of transition from the posterolateral (PL) to DL approach on reoperation and dislocation rates and patients’ reported outcome. Patients and methods — In a prospective cohort study between 2012 and 2015, we enrolled 362 patients (median age 83 years, 70% women, mean follow-up 25 months) with a displaced FNF. The first group of 146 patients were operated using the PL and the second group of 216 patients with a DL approach, after change of our routines. A multivariable Cox regression analysis was used to evaluate factors associated with dislocation and reoperation. A generalized linear model was used to evaluate the functional outcome by comparing WOMAC and Harris hip scores between the 2 groups. Results — The reoperation rate was reduced from 13% in the PL to 6% in the DL group and the dislocation rate from 13% to 4%. Cox proportional hazard analysis identified the PL approach as the only factor associated with an increased risk of reoperation (hazard ratio =2.5, 95% CI 1.2–5.2). Age, sex, ASA classification, type of arthroplasty, cognitive dysfunction, or the experience of the surgeon had no effect on the risk of reoperation. Patient-reported outcome was similar between the 2 groups. Interpretation — In patients with FNF we have reduced the reoperation and dislocation rates by changing the surgical approach used for hip arthroplasty without affecting the patient-reported functional outcome.