Introduction: The mechanobiology and response of bone formation to strain under physiological loading is well established, however investigation into exceedingly soft scaffolds relative to cancellous bone is limited. In this study we designed and 3D printed mechanically-optimised low-stiffness implants, targeting specific strain ranges inducing bone formation and assessed their biological performance in a pre-clinical in vivo load-bearing tibial tuberosity advancement (TTA) model. The TTA model provides an attractive pre-clinical framework to investigate implant osseointegration within an uneven loading environment due to the dominating patellar tendon force.

A knee finite element model from ovine CT data was developed to determine physiological target strains from simulated TTA surgery. We 3D printed low-stiffness Ti wedge osteotomy implants with homogeneous stiffness of 0.8 GPa (Ti1), 0.6 GPa (Ti2) and a locally-optimised design with a 0.3 GPa cortex and soft 0.1 GPa core (Ti3), for implantation in a 12-week ovine tibial advancement osteotomy (9mm). We quantitatively assessed bone fusion, bone area, mineral apposition rate and bone formation rate.

Optimised Ti3 implants exhibited evenly high strains throughout, despite uneven wedge osteotomy loading. We demonstrated that higher strains above 3.75%, led to greater bone formation. Histomorphometry showed uniform bone ingrowthin optimised Ti3 compared to homogeneous designs (Ti1 and Ti2), and greater bone-implant contact. The greatest bone formation scores were seen in Ti3, followed by Ti2 and Ti1.

Results from our study indicate lower stiffness and higher strain ranges than normally achieved in Ti scaffolds stimulate early bone formation. By accounting for loading environments through rational design, implants can be optimised to improve uniform osseointegration. Design and 3D printing of exceedingly soft titanium orthopaedic implants enhance strain induced bone formation and have significant importance in future implant design for knee, hip arthroplasty and treatment of large load-bearing bone defects.

Aim

Our aim was to evaluate the prevalence and impact of unexpected intraoperative cultures on the outcome of total presumed aseptic knee and hip revision surgery.

Summary Statement

Subject specific FE models of human Achilles tendon were developed and optimum material properties were found. Stress concentration occurred at the midsection but dependent on stiffening and thinning of tendon, indicating that they are two major factors for tendon rupture.

Background: Total knee replacement (TKR) failure is usually due to alignment, stability or fixation defects. Objective: To quantify the loads distribution using an absorptiometric method with two different tibial stems.

Methods: We analyzed 20 patients with cemented TKR, in two groups: one of them cylindrical and the other with cruciform stem. We studied the periprosthetic bony density evolution in three areas: under the stem, internal and external baseplate. We performed dual-energy x-ray absorptiometric (DEXA) measurements at 2, 3 and 7 years of follow-up.

Results: The evolution of the bony density under the internal baseplate to 2 and 3 years decreased from 0.920.20 to 0.900.19 g/cm2; under the external baseplate changed from 0.970.36 to 0.970.38 and under the stem raised from 1.050.25 to 1.080.26 in the cylindrical group. In the cruciform group, under the internal baseplate decreased from 0.750.08 to 0.710.05, under the external one decreased from 0.890.01 to 0.850.07 and under the stem changed from 1.060.06 to 1.040.29.

Comparing only the cylindrical subgroup (three missing patients), the DEXA measurements at 2, 3 and 7 years of follow-up were: 0.88, 0.84 and 0.80 g/cm2 under the internal baseplate; 0.79, 0.78 and 0.77 under the external one, and 0.99, 0.96 and 0.99 under the stem.

Conclusions: Loss of bony density is observed progressively after TKR. Comparativily, the diminution is greater for the cruciform stem. The internal compartment is more affected.

Don O’Donoghue (1950) described a particular acute injury of the knee in athletes (“also of high school age”) that he described as “an unhappy triad”. It consisted of: 1) rupture of the Medial Collateral Ligament (MCL), 2) damage to the Medial Meniscus (MM) and 3) rupture of the Anterior Cruciate Ligament (ACL)

We have reviewed the arthroscopic findings of 34 consecutive knees (ages 12 to 16 years) with complete rupture of the ACL. In 21 cases the injury was acute, and the remaining were chronic of had had more than one traumatic episode at the time of arthroscopy.

Out of the 34 cases, 26 had associated meniscal injuries: 4 MM; 14 Lateral Meniscus (LM) and 8 MM plus LM. Acute ACL injuries were associated mainly with LM damage (MM/LM: 1/5) whereas, in the chronic injuries, there were no such differences (MM/LM: 1/1). Out of the 21 acute LCA injuries there were 17 cases of acute rupture of the MCL.

Conclusions: 1- Contrary to what has been widely accepted, also in pre-adolescent and adolescent, Acute ACL ruptures are more frequently associated with LM damage that with MM tears. 2- Most injuries of the MM associated to ACL injuries (particularly “bucket handle” tears) are the result of a previously ACL unstable knee.

Purposes:

See if permanent damage of the growth plate after physeal distraction is the rule and

Introduction: Surgeons have always been concerned about the fate of the growth plate after physeal distraction and for that reason this technique has usually been considered only in patients nearing maturity. Previous experimental work has shown that the velocity of distraction has an influence on the viability of the growth plate at follow-up (recommended rate: 0.5 mm/day). Clinically, it has also been our observation that the condition of the physis prior to distraction is another important factor related to physeal function in the long term.

Patients and methods: Since 1987 we have used low velocity physeal distraction in 43 bone segments of which 37 cases have been followed-up at least for 24 months and this has been the group included in this study. The indications were lengthening (14), angular deformity correction (19) and resection of benign bone tumours (4). Most patients (24) were older than 10 y.o. and 22 of them were followed-up until maturity. We have retrospectively reviewed these patients looking at the radiological morphology and function of the distracted growth plate at follow-up.

Results: Out of the 24 children older than 10 y.o., twenty showed a premature complete physeal closure.

We looked with interest at the 13 cases younger than 10 y.o. since the repercussions of iatrogenic physeal damage would obviously be bigger in this age group. Five out of the 13 showed premature closure and in the remnant eight an open growth plate was observed at follow-up. All patients with open and/or functioning physes after distraction had no local injuries in the growth plate prior to distraction (4 congenital short femora and 4 normal physes). On the contrary, four out of the five cases with prematurely closed physes, had a local physeal damage prior to distraction (3 bony bridges and one non-union), and the remnant was a congenitally short femur. Growth after distraction was difficult to assess in the congenitally short femora but it has been very satisfactory in the 4 cases of previously normal physes (2 benign tumours and 2 femoral shortenings due to hip disorders). In three cases of congenital short femur in pre-teenagers we were able to repeat distraction twice through the same physis, since it had remained open after the first distraction.

Conclusions: Physeal premature closure often follows physeal distraction, but not always. The condition of the physis prior to lengthening is an important factor with influence on its viability after distraction.

Purpose: To assess the usefulness of Bone Transport and other “compression-distraction” systems for the treatment of Segmental Bone Defects (SBD) in patients younger than 16 years-old.

Patients and methods: This series includes 18 patients (12 boys, 6 girls) with SBD of the following etiologies: Post-traumatic defects with/without sepsis (14 cases) and post-resection defects (3 Congenital Pseudoartrosis of the Tibia -CPT- and 1 Aneurismal Bone Cyst). The age of the patients ranged from 8 to 16 years and the length of the defect from 5 cm to 13 cm except for one case (23 cm). The defect was located in the tibia in 14 cases and in the femur in four.

Nine patients (the longest defects) were treated by conventional Bone Transport whereas other compression-distraction techniques were used in the remaining. Monolateral frames were used in all cases. All but one of the post-traumatic cases had additional injuries and in four occasions one of the joints adjacent to the defect was involved.

Results: All cases healed, 6 with only one operation and 12 with more than one procedure. Healing time depended upon the length of the defect, age of the patient, etiology and occurrence of complications. Healing index also varied mainly depending on the etiology (CPT cases were slower) ranging form 1.5 to 0.7 months/cm. Bone graft at the compression site was used in 9 cases. Radiologically the most striking feature was the very early tubulization of the reconstructed segment along with the quick healing of the SBD.

The most frequent complication was pin tract infection (37%), one case needing change of pins. Fracture at the pin site was seen in two cases.

Functional results were closely related to: a. The healing of the defect and b. The existence of injuries to the joints adjacent to the defect.

With a minimum follow-up of 18 months there were 2 poor functional results due to an avascular necrosis of the dome of the talus (talus neck fracture).

Conclusion: These techniques are very useful in selected cases of large SBD in young patients. They have shown low morbidity, quick healing and, above all, very good remodeling potential. Associated injuries play a very important role in the final outcome of the treatment.

Introduction/objective: The results of Charnley total hip replacement, when performed in the general setting, may not be as good as expected (1). The objective is to know the long time survival in a Charnley low friction arthroplasty series performed in a General Hospital.

Material and methods: To have a minimum follow-up of ten years, we analysed 404 cases from a 431 series implanted in our department between 1976 and 1993. Mean age was 67 years, 57% were women.

The survival was calculated used Kaplan-Meier method, considering revision surgery as the analyzed event. Age and gender relation with survival were analyzed using the Log-Rank test.

Results: The survival of the Charnley low friction arthroplasty with the 95 % confidence interval was 92% (95–89%), 87% (90–81%), and 83% (89–78%) at 10, 15, and 20 years respectively. Patients younger than 60 years in the surgery time had lower survival than the older group for the acetabular (Log-Rank test p=0.043) and femoral components (Log-Rank test p=0,0085). There is not a statistically significant difference related to gender.

Conclusions: The survival in our low friction arthroplasties series at 10, 15, and 20 years is similar to the found in multicentric studies performed in other centres with special dedication to the surgery of the hip (2). Age affected the likelihood of long-term survivorship of the acetabular and femoral components used in Charnley low friction Arthroplasty.

Aims: To study the utility of a computer assisted orthopaedic surgery (CAOS) wireless system (navigator) in Total Knee Arthroplasty (TKA). Methods: Randomised prospective study. A sample of 40 TKA patients was randomised in two groups: CAOS was used in 20 of them. In the other group standard technique with manual alignment was performed. Femoral angle (formed between the femoral mechanical axis and the femoral component), tibial angle (formed between the tibial mechanical axis and the tibial platform) and femorotibial angle (formed between femoral and tibial mechanical axes) were measured from Computed Tomography Surviews taken in the immediate postoperative period. Results: In the standard group (without navigator) the femoral angle mean was 91.7° (ranged 90 to 94°). Tibial angle mean was 90.2° (87°–95°) and femorotibial angle mean was 175.9° (172°–180°) showing a slight prevalence of varus deviation of the extremity mechanical axis. In the group with navigator the femoral angle mean was 90.2∞ (87–93°), tibial angle mean 89.6°(85°–93°) and femorotibial angle mean 179.2° (177°–182°). There were statistically significant differences between groups for the femoral angle (p=0.001), and the femorotibial angle (p < 0.001). An ideal femorotibial angle (180±3°) was achieved for all the patients of the CAOS group but only 9 patients of the standard technique group reached this objective (p< 0.001). Conclusions: The use of CAOS for TKA favors the implant placement in a position nearer to the ideal mechanical axis.

A procedure is presented which allows the efficient production of a patient specific computer model of the femur, for surgical planning. Similar models require long processing times and/or high performance computing.

The method uses 24 key landmark points to customise a generic femur to patient data, using a desktop computer. By using non-linear elements a smooth, curved surface is obtained. A finite element mesh of a generic femur consisting of 384 elements was created using the analysis software CMISS (Bioengineering Institute, University of Auckland). A rectangular shaped host mesh was defined to enclose the generic femur. Datasets of 5 human femurs were obtained using a hand-held laser scanner on dry bones and the visible human dataset. Key landmark data points were selected on the generic femur along with corresponding target points on each data set. The host mesh was then deformed using a least squares algorithm, causing customisation of the generic femur to the patient specific model. Each customised model was compared with its entire dataset. The fitting process took less than 100 seconds on a 180 MHz 02 computer (SGI, CA, USA). The algorithm yielded an average root mean square (RMS) of 3.09mm with a standard deviation of 0.15mm. Operator time for positioning the projection points was less than 5 minutes.

This paper presents a novel means for customisation of human femoral geometry with generation of patient specific models on a PC from scan data in under 10 minutes. Current work is focusing on stress analysis, surgical simulation and planning.