18

• Mobility after unstable Lisfranc injury treated with temporary bridge plate fixation

Magnus Poulsen MD ¹, Are H. Stødle MD ¹, Stephan M. Röhrl MD PhD ¹. 1 Division of Orthopaedic Surgery, Oslo University Hospital, Oslo, Norway.

Objective: Recently, extra-articular, bridge plate fixation has gained popularity in the treatment of Lisfranc injuries. A temporarily stabilizing plate is expected to provide a more biomechanically favorable result compared to more traditional treatment options. The patient is estimated to regain joint mobility potentially reducing the risk of post-traumatic osteoarthritis. However, there are no published studies to validate this theory. Here we examine the range of motion in the 1st tarsometatarsal (TMT)-joint in patients treated with this surgical option.

Method: Eight patients with an unstable Lisfranc injury were included. All received similar surgical treatment, specifically a dorsal bridge plate over the 1st TMT joint and primary arthrodesis on the 2nd and 3rd TMT-joints. Tantulum markers were imbedded into the medial cuneiform and the 1st metatarsal bone. The bridge plate was removed four months post-operative. RSA images were taken one year post-injury to assess 1st TMT mobility. The radiographs were done laterally with the patient in a standing position with and without full weight-bearing. Sagittal dorsiflexion and translation were documented and compared between the two examinations. Precision was calculated as 1.96xSD.

Results: Precision for dorsiflexion and translation was respectively 1.1° and 0.6mm. All patients had 1st TMT dorsiflexion during weight-bearing (median 0.75°, range 0.12° – 2.39°). Median sagittal translation was 0.38 mm (range -0.26 – 1.85). However, only 2/8 patients had combined dorsiflexion >1.1° and translation >0.6mm in the 1st TMT joint. Control parameters included mean error (mean 0.07, range 0.04 – 0.30) and condition number (mean 76, range 48 – 109).

Conclusion: RSA can be applied to assess midfoot motion with comparable precision to other joints. In our study, 2/8 patients had motion in the 1st TMT one year after their Lisfranc injury.

19

• Trochanteric fractures treated with sliding hip screw with or without trochanteric stabilizing plate

Carl Erik Alm^1,2, Anders Karlsten, Frede Frihagen^2,3, Jan Erik Madsen^1,2, Lars Nordsletten^1,2 , Stephan M. Röhrl^{1. 1} Division of Orthopaedic Surgery, Oslo University Hospital, Oslo, Norway. ²Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway. ³Department of Orthopaedic Surgery, Østfold Hospital Trust, Grålum, Norway

Introduction: The role of the trochanteric stabilizing plate (TSP) in trochanteric fracture treatment remains unclear. The TSP has shown to increase stability in biomechanical studies, but the clinical evidence is scarce. Despite this, a sliding hip screw (SHS) with an additional TSP has been widely used for decades. The aim of this study was to compare stability and time to union of trochanteric fractures stabilised with a sliding hip screw with and without a TSP.

Material and method: 31 patients with AO 31-A2 fractures were randomized to a SHS with or without an additional TSP. 6-8 tantalum markers were implanted in both main segments and RSA-images was obtained before and after mobilization, and then at follow-up after 4, 8, 12, 26 and 52 weeks. Secondary fracture dislocation defined as total point migration, measured by RSA was the main outcome. All precision and migration analysis were performed using UmRSA Biomedical, Umeå, Sweden.

Results: At 1-year, median subsidence in the SHS group (n=8) was 7.29mm (range, 1.35 – 16.65) compared to 3.41mm (range, 0.78 – 13.48) in the SHS with TSP group (n=12). Median medialization of the femoral shaft was 1.67mm (range, 1.71 – 12.44) and 0.64mm (range, 0.96 – 9.85), while median secondary displacement in varus was 1.26^o (range, 5.00 – 35.38) and 0.71^o (range, 1.85 – 3.13) respectively. Total point migration was 8,22mm (range, 2.00–20.79)  and 4.00mm (range, 1.27 – 16.69).
Comparing medians, no statistically significant differences were found in either translation, rotation, or total point migration.

Interpretation and conclusion: No statistically significant differences in secondary fracture displacement were found between the treatment groups. We observed a tendency towards less secondary subsidence, medialization of the femoral shaft and varus in the TSP group. Whether this translates to better functional results must be examined with larger clinical trials.

Keywords: Trochanteric fractures, Trochanteric stabilizing plate, RSA, Migration

20

• Stable glenoid component of reversed shoulder arthroplasty at 2 years measured with model-based RSA

Alexander Nilsskog Fraser ^2,3Berte Bøe ¹_. Jan Erik Madsen ^1,2_. Tore Fjalestad ¹_. Stephan M. Röhrl ¹

¹ Division of Orthopaedic Surgery, Oslo University Hospital. ² Institute of Clinical Medicine; University of Oslo. ³ Diakonhjemmet Hospital

Introduction

Reverse total shoulder arthroplasty (TSA) is used for treating cuff arthropathy, displaced proximal humeral fractures and in revision shoulder surgery, despite sparse evidence on long-term results. Continuous RSA measured micro-migration of hip- and knee implants over two years indicates increased risk of implant loosening. Our intention was to conduct a stability analysis of the glenoid component in reverse TSA, using model-based RSA.

Materials and Methods

Twenty patients operated with reverse TSA at Oslo University Hospital in 2015-17 were included. RSA markers were placed in the scapular neck, the coracoid and the acromion. Reversed engineering (RE) has shown to be the preferred model-based RSA method, with a clinical precision of<0.25 mm for all translations (x, y, z) and<0.7° for rotations (x, z). RSA measurements were conducted postoperatively, at 3 months, 1 year, and 2 years. RSA analysis was performed using RSA Core with RE modality.

Results

Three men and 17 women were included, mean age 76 years. Thirteen patients had an acute PHF, two had delayed surgery for a PHF, one had a mal-union, three had cuff arthropathy, and one had a chronic shoulder dislocation. One patient was excluded due to revision surgery.  More than half of the patients displayed measurable migration in at least one degree of freedom at two years: six patients with linear translations below 1 mm and eight patients showed rotational migration. Except for one outlier, the measured rotations were below 2°. The migration pattern suggests implant stability at two years. Ten patients showed radiological signs of “notching”, and the mean OSS at two years was 29.2 points (15-36 points).

Conclusion

Model-based RSA with reversed engineering showed that the glenoid component of reversed TSA was stable at two years. The results indicate longevity of the implant, but further follow-up is required for this to be verified.

21

• Dynamic Radiostereometry Evaluation of Two Different Anterior Cruciate Ligament Reconstruction Techniques: Does Single Bundle Reconstruction plus Lateral Plasty Cause Knee Over-Constraint?

Di Paolo Stefano¹, Agostinone Piero², Pinelli Erika¹, Lucidi Gian Andrea², Bontempi Marco², Bragonzoni Laura¹, Zaffagnini Stefano ^1,2  1. University of Bologna, Bologna, Italy  2. 2nd Orthopaedic and Traumatologic Clinic, IRCCS Istituto Ortopedico Rizzoli, Italy

Introduction

Lateral extra-articular tenodesis (LET) in the context of Anterior Cruciate Ligament (ACL) reconstruction are adopted to better control anterolateral knee instability in patients with high-grade pre-operative pivot-shift. However, several authors believe these procedures are harmful to knee cartilage since they cause lateral compartment over-constraint in daily life motion.

The first aim of the present study was to identify kinematical differences between ACL-reconstructed knees with anatomic SB and SB plus lateral plasty (SBLP) techniques during the execution of an active under weight-bearing activity. The secondary aim was to compare these post-surgery kinematical data to the ones of the same knees before ACL reconstruction and of healthy contralateral knees.

Materials and Methods

Thirty-two patients (42 knees) were included in the study and divided in ACL-injured (n=32), anatomical SB (n=9), SBLP (n=18), and healthy knee (n=10) groups. Patients were asked to perform a single-leg squat before surgery and at minimum 18 months follow-up. Knee motion was determined using a validated model-based tracking process that matched subject-specific MRI bone models to dynamic biplane radiographic images, under the principles of Roentgen Stereophotogrammetric Analysis (RSA). Data processing was performed in a specific software developed in Matlab. Internal-External (IE), Varus-Valgus (VV) rotations, and Anterior-Posterior (AP) and Medio-Lateral (ML) translations were compared among the groups.

Results

No kinematical differences were found between SB and SBLP groups (p>0.05). A more medial tibial position (p<0.05) of the ACL-injured group was reported during the entire motor task and persisted after ACL reconstruction. Differences in IE and VV were found between injured ACL and healthy groups.

Interpretation and Conclusion

There were no relevant kinematical differences between SBLP and anatomic SB ACL reconstruction during the execution of a single-leg squat. Nonetheless, ACL reconstruction failed in restoring knee biomechanics regardless of the surgical technique.

Keywords

Dynamic RSA, ACL reconstruction, surgical techniques, kinematics

22

• Press-fit fixation of a conical shaped trapezium cup is superior in cortical compared to cancellous bone: A radiostereometric analysis in a pig bone model.

Janni Kjærgaard Thillemann^1,2, Lene Dremstrup¹, Torben Bæk Hansen^1,2 and Maiken Stilling^1,2

¹ University Clinic of Hand, Hip and Knee Surgery, Hospital Unit West, Holstebro, Denmark. ² Department of Clinical Medicine, Aarhus University, Incuba Skejby, Aarhus, Denmark.

Introduction: Cup failure has been a problem in trapeziometacarpal(TMC) arthroplasties. A stable primary press-fit bone fixation is important for achievement of later osseointegration of cementless implants. The articulating trapezium surface is usually cut, leaving a leveled cancellous surface for cup insertion. The cortical bone is stronger, but cup insertion into a saddle-shaped surface may be challenging.

We aimed to compare primary cancellous and cortical press-fit fixation of a new conical-shaped TMC cup design, and to investigate the effect of cup diameter.

Material and methods: Thirty-two hydroxyapatite-coated conical cup designs of 9mm and 10mm were randomly allocated to cancellous or cortical bone fixation. The saddle-shaped bone from pig forefeet were dissected, six tantalum beads of 1mm were inserted, and the bones were rigidly fixed in epoxy-glue before the cups were inserted with press-fit fixation. Cup migration was evaluated with static radiostereometric(RSA) radiographs, recorded at baseline and after cyclic-load tests, performed from 150N to 1050N. Precision was evaluated by RSA double-examinations. Total translation(TT) was calculated, and cup-failure was defined as TT >0.5mm, between two pressure-load tests.

Results: Precision of TT was 0.09mm and random error was 0.12mm. Below 750N load, migration of all cups was below 0.5mm TT between each load-cycle, but TT of cups with cancellous bone fixation was up to 0.25mm(95% CI 0.12; 0.37) higher compared to cups with cortical bone fixation(p<0.04).

In 9mm cups, 250N pressure-load on cancellous fixated cups resulted in a higher TT, compared to cortical fixated cups(p=0.001), whereas the 10 mm cups required 550N pressure-load to detect a difference(p=0.008).

The Kaplan-Meier cumulative survival estimate at 1050N, was best for 10mm cups with cortical bone fixation(88%) of and least for 9mm cups with cancellous bone fixation(13%).

Conclusion:  Based on this experimental study, the largest possible size conical shaped cup in addition to cortical bone fixation, is advised for total TMC joint arthroplasty surgery.