Niklaus F. Friederich

Bone screws are used in orthopaedic surgery for fracture fixation. Correctly torquing the screws is important for fixation quality. Over-tightening may strip the threads, while under-tightening may result in loosening over time. This paper focuses on testing an approach where strength is estimated using screw insertion data from torque and rotation sensors, and stripping torque is predicted based on this strength. A common type of bone screw was inserted until stripping 10 times each into 8 types of polyurethane surrogate for bone. The torque–rotation data from the insertion was used to identify the material strength and estimate the stripping torque and compared with the experimental maximum torque. A good relationship was found between the estimated/predicted and true stripping torques (r = 0.926, 95% confidence interval (C.I.) [0.886, 0.952]), with a mean error of 18%. Additionally, the intermediate identified strength values were found to be highly correlated with the data-sheet values for the materials (r = 0.977, 95% C.I. [0.964, 0.985]). These outcomes demonstrate the viability and significance of this concept in general, although more development and testing is required for broad clinical applicability; such tests would be extended for more types of bone screws and use a large set of human bone samples to better reflect the natural variability.

In the field of osteotomy, the use of lasers has been studied for several years;^{1 – 8} however, some early clinical studies showed severe collateral damage and a prolonged healing process.⁹ In response, efforts have been made to optimize laser systems intended for laserosteotomy. For example, modern Er:YAG laser systems have been used to remove intraoral hard tissue in humans, without showing damage in subsequent histological analyses.¹⁰ More recent studies have shown how the use of new irrigation and temperature feedback detection systems for Er:YAG laserosteotomy can help achieve safe, deep bone ablation.¹¹ Other results from a robotic free-space laser device, CARLO^®, based on an Er:YAG laser, show potential for use in osteotomy applications. The CARLO laser device was used for the first clinical bone surgery worldwide, where the functionality of the patient’s jaw was improved. After years of investigation in the field, the device was used in July 2019 for an in vivo mid-face osteotomy at the Department of Oral Maxillofacial Surgery, University Hospital Basel, Switzerland.^7,12,13

In the above-named article (ibid., vol. 68, no. 8, pp. 2412–2422, Aug. 2021, doi: 10.1109/TBME.2020.3041512) Fig. 1 is not correct. The correct version is provided here.

Objective: Developing robotic tools that introduce substantial changes in the surgical workflow is challenging because quantitative requirements are missing. Experiments on cadavers can provide valuable information to derive workspace requirements, tool size, and surgical workflow. This work aimed to quantify the volume inside the knee joint available for manipulation of minimally invasive robotic surgical tools. In particular, we aim to develop a novel procedure for minimally invasive unicompartmental knee arthroplasty (UKA) using a robotic laser-cutting tool. Methods: Contrast solution was injected into nine cadaveric knees and CT scans were performed to evaluate the tool manipulation volume inside the knee joints. The volume and distribution of the contrast solution inside the knee joints were analyzed with respect to the femur, tibia, and the anatomical locations that need to be reached by a laser-cutting tool to perform bone resection for a standard UKA implant. Results: Quantitative information was determined about the tool manipulation volume inside these nine knee joints and its distribution around the cutting lines required for a standard implant. Conclusion: Based on the volume distribution, we could suggest a possible workflow for minimally invasive UKA, which provides a large manipulation volume, and deducted that for the proposed workflow, an instrument with a thickness of 5-8 mm should be feasible. Significance: We present quantitative information on the three-dimensional distribution of the maximally available volume inside the knee joint. Such quantitative information lays the basis for developing surgical tools that introduce substantial changes in the surgical workflow.

The introduction of a standardized SPECT/CT algorithm including a localization scheme, which allows accurate identification of specific patterns and thresholds of SPECT/CT tracer uptake, could lead to a better understanding of the bone remodeling and specific failure modes of unicondylar knee arthroplasty (UKA). The purpose of the present study was to introduce a novel standardized SPECT/CT algorithm for patients after UKA and evaluate its clinical applicability, usefulness and inter- and intra-observer reliability. Tc-HDP-SPECT/CT images of consecutive patients (median age 65, range 48–84 years) with 21 knees after UKA were prospectively evaluated. The tracer activity on SPECT/CT was localized using a specific standardized UKA localization scheme. For tracer uptake analysis (intensity and anatomical distribution pattern) a 3D volumetric quantification method was used. The maximum intensity values were recorded for each anatomical area. In addition, ratios between the respective value in the measured area and the background tracer activity were calculated. The femoral and tibial component position (varus-valgus, flexion-extension, internal and external rotation) was determined in 3D-CT. The inter- and intraobserver reliability of the localization scheme, grading of the tracer activity and component measurements were determined by calculating the intraclass correlation coefficients (ICC). The localization scheme, grading of the tracer activity and component measurements showed high inter- and intra-observer reliabilities for all regions (tibia, femur and patella). For measurement of component position there was strong agreement between the readings of the two observers; the ICC for the orientation of the femoral component was 0.73-1.00 (intra-observer reliability) and 0.91-1.00 (inter-observer reliability). The ICC for the orientation of the tibial component was 0.75-1.00 (intra-observer reliability) and 0.77-1.00 (inter-observer reliability). The SPECT/CT algorithm presented combining the mechanical information on UKA component position, alignment and metabolic data is highly reliable and proved to be a valuable, consistent and useful tool for analysing postoperative knees after UKA. Using this standardized approach in clinical studies might be helpful in establishing the diagnosis in patients with pain after UKA.

Purpose: The primary purpose of our study was to analyse the long‐term outcome of patients treated for anterior cruciate ligament (ACL) tears by anatomical single‐bundle ACL reconstruction with patellar tendon autograft. The secondary purpose was to identify predictive factors for good outcome and occurrence of osteoarthritis.Methods: Sixty‐three patients (m:f = 54:9; mean age at surgery, 27 ± 7 years) treated by ACL reconstruction were evaluated with a mean follow‐up of 16 ± 1 years using IKDC2000, the SF36, Lysholm and Tegner score, Knee Society score, visual analogue scale for pain and satisfaction and KOOS. The femoral tunnel position was evaluated according to Sommer. It was also assessed in percentage of the Blumensaat line and the tibial tunnel position in percentage of the total anterior–posterior plateau length. The extent of osteoarthritis was graded according to the Kellgren–Lawrence score.Results: The total IKDC2000 was normal in 20 (32 %), nearly normal in 29 (46 %), abnormal in 12 (19 %) and severely abnormal in 3 (5 %) of patients. The mean total SF‐36 was 89 ± 13, the Lysholm score 95 ± 12, the Knee Society score 191 ± 16 and the total KOOS 84 ± 19. The Tegner score decreased from pre‐injury 7(4–10) to 6 (2–10) at follow‐up. The Kellgren–Lawrence score was normal in 17 (27 %), suspected osteoarthritis in 25 (40 %), minimal osteoarthritis in 5 (8 %), moderate osteoarthritis in 9 (14 %) and severe osteoarthritis in 3 patients (5 %). The femoral tunnel was in zone A in 43 patients (68 %), in zone B in 16 (25 %) and in zone C in 4 patients (7 %). The femoral tunnel position in percentage of the Blumensaat line was 49 ± 3 (range, 44–57), and the tibial tunnel position in percentage of the total anterior–posterior plateau length was 32 ± 6 (range, 21–46). Patients with meniscal lesion at the time of ACL tear showed significantly less favourable outcomes than those without.Conclusions: Patients treated by the proposed ACL reconstruction technique showed on average good to excellent long‐term results. A meniscal lesion at the time of ACL tear was highly predictive for less favourable outcome.Level of evidence: IV.

Background: One major concern in the treatment of ACL lesions in children and adolescents with open physes is the risk of iatrogenic damage to the physes and a possibly resulting growth disturbance. Purpose: The primary purpose of this article is to describe our technique of a transphyseal ACL reconstruction using quadriceps tendon-bone autograft in children and adolescents with open growth plates. The secondary aim is to report our early results in terms of postoperative growth disturbances which are considered to be a major concern in this challenging group of patients. It was our hypothesis that with our proposed technique no significant growth disturbances would occur. Methods: From January 1997 to December 2007 49 consecutive children and adolescents with open growth plates were treated for a torn ACL using the aforementioned surgical technique. The patients (28 males and 21 females) with a median age at surgery of 13 (range 8-15) years were retrospectively evaluated. Outcome measures were follow-up radiographs (weight-bearing long leg radiographs of the injured and uninjured knee, anteroposterior and lateral views, a tangential view of the patella and a tunnel view of the injured knee) and follow-up notes (6 weeks, 3, 6, 12 months and until closing of physes) for occurrence of any tibial and/or femoral growth changes. Results: All of the 49 patients had a sufficient clinical and radiological follow-up (minimum 5 years, rate 100%). 48 cases did not show any clinical and radiological growth disturbance. One case of growth disturbance in a 10.5 years old girl was observed. She developed a progressive valgus-flexion deformity which was attributed to a malplacement of the autograft bone block within the femoral posterolateral epiphyseal plate leading to an early localized growth stop. None of the patients were reoperated due to ACL graft failure. Five of the patients underwent revision ACL surgery due to another adequate sports trauma after the growth-stop. The tibial fixation screw had to be removed under local anaesthesia in 10 patients. Conclusions: The described ACL reconstruction technique represents a promising alternative to previously described procedures in the treatment of children and adolescents with open growth plates. Using quadriceps tendon future graft availability is not compromised, as the most frequently used autograft-source, ipsilateral hamstring tendons, remains untouched.