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. 2022 Mar;8(1):117–131. doi: 10.21037/jss-21-100

Table 1. Summary of findings from all 18 included studies.

Study Study population Application Device design Recorded force on implants
Rohlmann et al. (1995) 1 patient with degenerative instability Measuring in vivo implant loads after surgery Dick internal fixators (rods) modified with six strain-gauges, telemetry unit, inductive coil hermetically sealed in a cartridge. Walking: AF =−170, BM=− 2.7
Lifting leg whilst supine: AF =−210, BM =−2.9
Lateral flexion whilst supine: AF =−240, BM =−2.2
Left hand to right knee whilst supine: AF =−125, BM =−1.9
Cycling whilst supine: AF =−245, BM =−3.4
Rohlmann et al. (1997) 5 lumbar cadaver spines. 3 patients (1 with degenerative instability, 2 with compression fractures) Comparing in vitro and in vivo implant loads Modified Dick internal fixators as above In vitro
Standing: AF =−150, BM =−4.5
Flexion: AF =−40, BM =−3.5
Extension: AF =−60, BM =1.5
Patient 1
Standing: AF =−210, BM =−6
Flexion: AF =−220, BM =−6.5
Extension: AF =−270, BM =−6
Patient 2
Standing: AF =−140, BM =−1.5
Flexion: AF =−150, BM =−1.5
Extension: AF =−160, BM =−2
Patient 3
Standing: AF =−130, BM =−6
Flexion: AF =−160, BM =−6.5
Extension: AF =−150, BM =−6.5
Rohlmann et al. (1997) 1 patient with degenerative instability. 1 patient with a compression fracture Measuring in vivo loads during walking Modified Dick internal fixators as above Relative bending moments
From seated position: standing =100%, ventral flexion =105%, extension =107%, lateral bending =108%, axial rotation =108%
Whilst standing: sitting down =119%, tip toes =110%, ventral flexion =127%, extension =124%, lateral bending =118%, axial rotation =115%, elevation of extended arm =110%, kneeling on hands and knees =69%, kneeling + flexion =97%, kneeling + extension =80%, kneeling + leg extension =100%
Rohlmann et al. (1998) 2 patients with compression fractures. 1 patient with degenerative instability Measuring the influence of muscle forces on implant loads Modified Dick internal fixators as above Left fixator
Relaxed: AF =140, BM =4.2
Abdominal muscle: AF =250, BM =7.2
Back muscle: AF =280, BM =7.2
Pressing: AF =150, BM =5.2
Coughing: AF =145, BM =4.3
Right fixator
Relaxed: AF =60, BM =1
Abdominal muscle: AF =55, BM =1.5
Back muscle: AF =190, BM =4.2
Pressing: AF =70, BM =2.4
Coughing: AF =90, BM =2.4
Rohlmann et al. (1999) 7 patients with compression fractures. 3 patients with degenerative instability Measuring in vivo loads in different body positions Modified Dick internal fixators as above Patient 1
Standing: AF (left) =−224, AF (right) =−125, BM (left) =−6.438, BM (right) =−4.143
Sitting: AF (left) =−161, AF (right) =−133, BM (left) =−6.122, BM (right) =−4.239
Supine: AF (left) =−77, AF (right) =−85, BM (left) =−2.464, BM (right) =−0.586
Prone: AF (left) =−102, AF (right) =−89, BM (left) =−3.280, BM (right) =−1.219
Lateral: AF (left) =−72, AF (right) =−95, BM (left) =−3.178, BM (right) =−1.668
Patient 2
Standing: AF (left) =−203, AF (right) =−109, BM (left) =−0.502, BM (right) =−3.769
Sitting: AF (left) =−187, AF (right) =−85, BM (left) =−0.370, BM (right) =-3.271
Supine: AF (left) =−96, AF (right) =−100, BM (left) =0.129, BM (right) =−3.243
Prone: AF (left) =−100, AF (right) =−99, BM (left) =0.257, BM (right) =−3.082
Lateral: AF (left) =−95, AF (right) =−91, BM (left) =0.663, BM (right) =−3.037
Patient 3
Standing: AF (left) =−141, AF (right) =−111, BM (left) =−4.861, BM (right) =−4.610
Sitting: AF (left) =−111, AF (right) =−81, BM (left) =−4.294, BM (right) =−3.927
Supine: AF (left) =−12, AF (right) =−21, BM (left) =−1.239, BM (right) =− 1.345
Prone: AF (left) =−20, AF (right) =−29, BM (left) =−1.538, BM (right) =−1.974
Lateral: AF (left) =−54, AF (right) =−28, BM (left) =−2.222, BM (right) =−1.795
Rohlmann et al. (2000) 7 patients with compression fractures. 3 patients with degenerative instability Measuring in vivo loads during sitting, standing, walking, and lying in the first 20 post-operative months Modified Dick internal fixators as above Marked interindividual differences in fixator loads
Szivek et al. (2005) 1 patient with spinal deformity Monitoring fusion progress, measuring strain on spine during cantilever bending Calcium phosphate ceramic (CPC)-coated strain gauges attached on lamina, uncoated single-element gauge to left rod with a subminiature, remotely powered radio transmitter Control (non-instrumented)
T7 lamina: left =80 μ-strain, right =−180 μ-strain
T9 lamina: left =120 μ-strain, right =90 μ-strain
T9 vertebral body: left =−405 μ-strain, right =−270 μ-strain
T11 vertebral body: left =−320 μ-strain, right =−280 μ-strain
Instrumented
T7 lamina: left =3 μ-strain, right =−3 μ-strain
T9 lamina: left =80 μ-strain, right =2 μ-strain
T9 vertebral body: left =−480 μ-strain, right =−190 μ-strain
T11 vertebral body: left =−190 μ-strain, right =−280 μ-strain
Rod: left =270 μ-strain, right =220 μ-strain
PMMA fused
T7 lamina: left =−30 μ-strain, right =−390 μ-strain
T9 lamina: left =−195 μ-strain, right =−180 μ-strain
T9 vertebral body: left =−280 μ-strain, right =−270 μ-strain
T11 vertebral body: left =−190 μ-strain, right =−120 μ-strain
Rod: left =190 μ-strain, right =230 μ-strain
Rohlmann et al. (2008) 2 patients with compression fractures of L1 Measuring in vivo loads during sitting, standing, walking, and lying in the first 6 post-operative months Modified VBR SynexTM, a VBR with a hollow cylinder housing sensor, inductive power coil and telemetry unit AF for different positions: Lying ≤100, Standing/sitting =150–450, Flexion ≥420, Elevation of arms to 90° with weight ≥700
BM for most exercises ≤2
Rohlmann et al. (2008) 3 patients with compression fractures of L1 Measuring in vivo loads during sitting, standing, walking, and lying in the first post-operative month Modified VBR SynexTM Relative AF to standing§: standing =100%, flexion =242%, extension =34%, lateral bending =127%, axial rotation =104%, elevation of both arms to 90° =194%, abduction of both arms 90° =108%, walking upstairs =217%, walking downstairs =169%, sitting =99%, sitting + flexion =229%, lying supine =14%, lying prone =22%, lying lateral =26%
Relative BM to standing: standing =100%, flexion =272%, extension =37%, lateral bending =246%, axial rotation =133%, elevation of both arms to 90° =203%, abduction of both arms 90° =100%, walking upstairs =219%, walking downstairs =160%, sitting =122%, sitting + flexion =256%, lying supine =45%, lying prone =47%, lying lateral =51%
Rohlmann et al. (2010) 4 patients with A3 type compression fractures Measuring in vivo loads on spine during whole-body vibration Modified VBR SynexTM Maximum force increased with increasing intensity of vibration
At maximum intensity vibration (three-axes), the average increase in force on VBR ranges from 123–189%
Leaning backwards decreased implant loads to approximately 50% of the force in normal sitting
Rohlmann et al. (2011) 5 patients with A3 type compression fractures Measuring in vivo loads on spine during sitting Modified VBR SynexTM Average change in force whilst sitting: 15° flexion =48% increase, 10° extension =19% decrease
Relative reduction in force compared to sitting on stool: bench =7%, stool with padded wedge =9%, knee stool =19%, chair =35%, office chair =41%
Rohlmann et al. (2012) 5 patients with A3 type compression fractures Measuring in vivo loads on spine during position changes Modified VBR SynexTM Maximum force on VBR relative to standing (according to recommendation): lateral to supine to lateral =110%, lateral to prone to lateral =130%, lateral lying to sitting =390%, sitting to lateral lying =395%
Maximum force on VBR relative to standing (not according to recommendation): lateral to supine to lateral =425%, lateral to prone to lateral =155%, lateral lying to sitting =405%, sitting to lateral lying =625%
Rohlmann et al. (2013) 5 patients with A3 type compression fractures Measuring the effect of orthosis on VBR load Modified VBR SynexTM Average decrease in resultant force on VBR, lumbo tristep brace =9%, hyperextension orthosis =19%
Rohlmann et al. (2013) 5 patients with A3 type compression fractures Long-term monitoring up to 65 months Modified VBR SynexTM Significant inter-patient variation
Force for walking was higher than standing by an average of 100N or 71%
Rohlmann et al. (2014) 5 patients with A3 type compression fractures Measuring in vivo loads on spine during activities of daily living Modified VBR SynexTM Ten activities with the highest resultant force: lifting weight from ground =545–1,229 N, forwards arm elevation with weight =611–972 N, moving weight in front of body=758–1,126 N, standing up/sitting down =206–681 N, staircase walking =305–726 N, tying shoes =585–926 N, upper body flexion =341–844 N, lifting a carried weight =261–690 N, washing face =712–831 N, moving from lying to sitting =170–858 N, walking =129–498 N
Dreischarf et al. (2015) 5 patients with A3 type compression fractures Measuring in vivo loads on spine during forward bending Modified VBR SynexTM Maximal force of 450 N measured whilst returning to initial standing position from maximal inclination angle of 53°
Flexion during standing (330 N) > flexion during sitting (200 N)
Damm et al. (2017) 5 patients with A3 compression fractures Measuring in vivo loads on spine and hip during forward bending Modified VBR SynexTM Average peak force in VBR during walking =39% of bodyweight
Force on implants during walking: hip, knee > spine
Barri et al. (2021) Polymer testing blocks Monitoring fusion progress Fowler-Nordheim (FN) sensor data-logger on rods Decrease in measured voltage corresponds with increasing elastic modulus (modelling fusion)

, all AF values are represented in N and BM values are represented in Nm unless otherwise stated; , results from 3 out of 10 patients are reported. Each patient pertains to one of three surgical indications for Dick internal fixators: ‘degenerative instability’, ‘old vertebral fracture’, ‘fresh vertebral fracture’; §, results for 1 patient out of 2 reported; , results for 1 patient out of 5 reported. AF, axial force; BM, bending moment; VBR, vertebral body replacement.