Double-threaded Screws Research Articles

Scaphoid fractures : Current diagnostic and treatment concepts

Scaphoid fractures are by far the most frequent fractures of the carpal bones of the hand and often lead to problematic healing processes if the diagnostics and treatment are inadequate. The main complication of ascaphoid fracture is pseudarthrosis, which leads to carpal collapse and degenerative arthritis of the wrist if left untreated. Early diagnosis and individualized differentiated treatment aim to achieve bony healing with restoration of the scaphoid shape and preservation of the function of the wrist. The anatomical and biomechanical characteristics of the scaphoid can impede bony healing after afracture and, in contrast to the diagnostics and treatment, cannot be influenced. Ahistory of trauma and typical clinical signs of ascaphoid fracture should lead to systematic imaging diagnostics with obligatory computed tomography. Only by determining the exact fracture morphology can an appropriate treatment concept be established. Conservative treatment should be restricted to stable fractures without relevant displacement. Fractures of the proximal scaphoid pole are considered unstable even if they are not displaced. Operative treatment is indicated for all unstable fractures. The favored surgical procedure is osteosynthesis with acannulated double-threaded screw, which can be used in aretrograde or antegrade manner and in aminimally invasive or open technique, depending on the fracture type. Surgical treatment results in earlier bony healing and quicker restoration of function but can be associated with ahigher complication rate. Posttraumatic osteoarthritis after healing in malalignment is usually asymptomatic.

Minimal invasive Hallux valgus Korrektur über intraartikuläre perkutane Chevron Akin-Osteotomie (PECA)

BackgroundThe minimally invasive correction of hallux valgus is also becoming increasingly popular in German-speaking countries. Numerous percutaneous techniques for correcting the first ray have been published in recent years. To this day, there is still no clarity about the benefits of each technique. Material and MethodsFrom 2019 to 2021, a percutaneous intra-articular Chevron-Akin osteotomy (PECA) with fixation of the metatarsal osteotomy via a double-threaded screw was performed on 70 feet. The radiological parameters (intermetatarsal angle, hallux valgus angle) and the American Orthopedic Foot and Ankle score (AOFAS) were evaluated pre- and postoperatively. ResultsAfter a mean follow-up of 6 months, the radiological parameters were significantly improved. The intermetatarsal angle improved from 13.1° to 5.9°, the hallux valgus angle from 27.4° to 9.3°. The AOFAS improved from 51.4 points preoperatively to 91.2 points postoperatively. There were 2 relevant complications in the group studied, a screw irritation necessitating early metal removal and a secondary dislocation of the 1st metatarsal head necessitating open revision. ConclusionsThe results show the good correction potential of the PECA technique used to treat a mild to moderate hallux valgus deformity. However, further investigations with long-term results and studies comparing the various established percutaneous distal osteotomy procedures are urgently needed in order to increase the comparability of the different procedures.

Development and biomechanical test of a new pedicle screw for thoracolumbar spinal surgery

Rupture of the medial pedicle wall often occurs during pedicle screw insertion. This allows the pedicle screw to compress or cut the nerve root and/or spinal cord. In this paper, we designed a new double-threaded pedicle screw that has a cylindrical outer diameter and a conical core diameter, with a wide thread at the front, no thread in the middle, and a narrow thread at the rear, according to an analysis of the shortcomings of the conventional pedicle screw and anatomical parameters in 300 healthy adult volunteers. After the screw was placed, the non-threaded portion of the screw was located at the vertebral pedicle. No nerve root cutting occurred if the screw was misplaced and the medial wall of the vertebral pedicle was broken. We then performed biomechanical tests using a static universal testing machine and compared the new double-threaded screws with the conventional full-threaded pedicle screws, however, the differences were not obvious. In compression bending fatigue tests, the novel double-threaded pedicle screws were subjected to 5 million fatigue cycle loads without failure. The current study demonstrated that the new pedicle screw possesses similar biomechanical features as those of the conventional fully threaded pedicle screw. This provides a basis for further clinical applications.

Bone Coverage around Hydroxyapatite/Poly(L-Lactide) Composite Is Determined According to Depth from Cortical Bone Surface in Rabbits.

Composites of unsintered hydroxyapatite (HA) and poly(L-lactide) (PLLA) reinforced by compression forging are biodegradable, bioactive, and have ultrahigh strength. However, foreign body reactions to PLLA and physical irritation can occur when not covered by bone. We aimed to confirm the relationships between the depth of the implanted HA-PLLA threaded pins and the new bone formation. We inserted HA-PLLA composite threaded pins (diameter: 2.0 or 4.5 mm) into the femoral and tibial bones of 32 mature male Japanese white rabbits (weight 3.0–3.5 kg) with the pin head 1 or 0 mm below or protruding 1 or 2 mm above surrounding cortical bone. Eight euthanized rabbits were radiologically and histologically assessed at various intervals after implantation. Bone bridging was complete over pins of both diameters at ~12 weeks, when inserted 1 mm below the surface, but the coverage of the pins inserted at 0 mm varied. Bone was not formed when the pins protruded >1 mm from the bone surface. No inflammation developed around the pins by 25 weeks. However, foreign body reactions might develop if composites are fixed above the bone surface, and intraosseous fixation would be desirable using double-threaded screws or a countersink to avoid screw head protrusion.

Minimally Invasive vs Open Akin Osteotomy.

Minimally invasive techniques of Akin osteotomy have grown in popularity, as early results suggest faster recovery, earlier return to work, and minimized wound healing problems. Preserving lateral cortex integrity during first phalanx osteotomy thereby presents a challenge because of the lack of direct visual control. This retrospective comparative study investigated clinical and radiographic outcomes of minimally invasive and open Akin osteotomy with different fixation methods and analyzed whether or not intraoperative violation of the lateral cortex caused loss of correction or delayed bone healing. One hundred eighty-four patients (210 feet) with symptomatic hallux valgus and pathologic interphalangeal angle (IPA) of at least 10 degrees underwent surgery combined with Akin osteotomy. Minimally invasive Akin osteotomies were fixed in 124 feet with 2 crossing percutaneous K-wires and compared to 86 Akin osteotomies by open technique with double-threaded (head and shank) screw fixation. At 1 day and 6 and 12 weeks postoperatively, IPA and bony consolidation were radiographically and clinically assessed. Mean preoperative IPA was 13.4 ± 3.6 degrees in minimally invasive (MI) and 13.3 ± 3.5 degrees in open surgery (OS) cases (P > .05). Intraoperative breach of the lateral cortex occurred in 12 (13.9%) in OS and 64 (51.6%) in MI cases. Whereas the breach occurred in open technique mainly during manual correction by applying a medial closing force, it was caused predominantly by the use of the burr in minimally invasive technique. After 12 weeks, the mean IPA was 4.1 ± 1.4 degrees in MI and 4.8 ± 1.2 degrees in OS cases (P > .05). Bony consolidation was complete after 6 and 12 weeks in OS and MI, respectively. Three deep infections occurred in the OS Group after Lapidus arthrodesis and 2 deep infections were registered in the MI Group after minimally invasive chevron and Akin osteotomy. The infections were not at the site of the Akin osteotomy. Breach of the lateral cortex did not impair bone healing or correction of IPA. Minimally invasive Akin osteotomy with K-wire fixation provided equivalent correction of IPA compared to open surgery with screw fixation. Level III, retrospective comparative series.

Biomechanical comparison of three different compression screws for treatment of odontoid fractures evaluation of a new screw design

BackgroundLag screw osteosynthesis in odontoid fractures shows a high rate of pseudarthrosis. Biomechanical properties may play a role with insufficient fragment compression or unnoticed screw stripping. A biomechanical comparison of different constructed lag-screws was carried out and the biomechanical properties determined. MethodsTwo identical compression screws with different pilot holes (1.25 and 2.5 mm), a double-threaded screw and one sleeve-nut-screw were tested on artificial bone (Sawbone, densities 10-30pcf). Fragment compression and torque were continuously measured using thin-film force sensors (Flexiforce A201, Tekscan) and torque sensors (PCE-TM 80, PCE GmbH). FindingsThe lowest compression reached the double-threaded screw. Compression and sleeve-nut-screw achieved 214–298% and 325–546%, respectively, of the compression force of double-threaded-screw, depending on the test material. The pilot hole optimization led to a significant improvement in compression only in the densest test material. Screw stripping took place significantly later with increasing density of the test material on all screws. In compression screws this was done at a screw rotation of 180–270°, in sleeve nut screw at 270–720° and in double-threaded screws at 300–600° after reaching the maximum compression. InterpretationDouble-threaded screw is robust against screw stripping, but achieves only low fragment compression. The classic compression screws achieve better compression, but are sensitive to screw stripping. Sleeve-nut screw is superior in compression and as robust as double-threaded screw against screw stripping. Whether the better biomechanical properties lead to a reduction in pseudarthrosis must be proven in clinical trials.

Influence of the rope effect on the slip curve of laterally loaded, nailed and screwed timber-to-timber connections

Timber-to-timber connections with different types of screws and nails were experimentally investigated with the aim to quantify the contribution of their axial resistance to their slip and their lateral load bearing capacity, which is the so-called rope effect in dowel-type timber connections. Five different types of screws, including partly threaded and double-threaded screws, as well as three types of nails, including smooth round nails, twisted square-sectioned and grooved nails, were used in the experimental investigations in order to cover a broad range of axial resistance of fasteners. Their behavior was tested in single shear and double shear timber-to-timber connections. In addition to connection testing, system and material properties were experimentally determined. This gave input to design equations and allowed for a comparison of the mechanical model in the European design standard for timber structures, Eurocode 5, with experiments. Experiments indicate that the initial slip modulus in the quasi-elastic domain is not influenced by withdrawal capacity of the fastener, while it shows pronounced influence on load-carrying capacity and the nonlinear shape of the slip curve of the connection at larger deformations. Rope effect strongly depends on fastener properties. High axial resistance of fasteners leads to highly non-linear slip curves and design equations tended to underestimate strength including the rope effect up to a displacement limit of 15 mm. Experimentally observed failure modes were well in line with the theoretical failure modes predicted by the design model. The provided experimental results are motivation for improvement of design models and development of analytical and numerical models that account for nonlinear effects in the complex load transfer mechanism.

Arch-shaped approach : New modified medial approach for the treatment of talus fractures

Anatomical reduction and fixation of complex talar fractures (Hawkins typeIII andIV, Marti typeIII andIV) using amedial approach. Displaced talar fractures (Hawkins typeIII andIV, Marti typeIII andIV) with the need for amedial malleolar osteotomy or the simultaneous treatment of amedial malleolus fracture. High perioperative risk, severe soft tissue injuries in the medial approach area, infected soft tissues. Medial arch-shaped approach about 12 cm in length over the medial malleolus using asimultaneous medial malleolus fracture or via an additional medial malleolar osteotomy. Dissection and retraction of the terminal branches of the saphenous vein and the saphenous nerve. Protection of the blood supply in the area of the medial talus and in the sinus tarsi. Reduction of the talar joint surfaces and reconstruction of the anatomical axes according to the preoperative planning by means of native radiological and computed tomographic imaging. Osteosynthesis adapted to the fracture type using Kirschner wires, conventional screws, cannulated screws, double-threaded screws, resorbable pins, magnesium screws, small fragment plates. Lower leg splint or orthesis for 6weeks, partial weight-bearing with 20 kg for 10-12weeks. Early range of motion exercise of the ankle, subtalar and mid-tarsal joints. In the past 5years, 11patients with either Hawkins typeIII andIV or Marti typeIII andIV fractures were treated operatively using the arch-shaped approach. No soft tissue problems were seen related to the arch-shaped approach. Of the 7patients who could be followed up after an average of 2years, the mean American Orthopedic Foot and Ankle Score was73. Avascular necrosis occurred in 3cases (43%). These were partial necroses of less than one third of the talar body with asymptomatic course at the time of examination. In 4patients (57%) radiographic signs of osteoarthritis occurred within 2years, whereby in two of those cases (29%) an arthrodesis of the upper ankle was performed.

Headless double-threaded compression screws plus microplate for capitellar fracture of Ring typeII

Objective To investigate the clinical effects of headless double-threaded compression screws plus microplate for treatment of capitellar fracture of Ring type Ⅱ. Methods In the period from March 2015 to February 2018, 12 capitellar fractures of Ring type Ⅱ were treated at Department of Upper limb Orthopedics, Zhengzhou Orthopaedics Hospital. There were 8 men and 4 women, aged from 25 to 57 years (average, 35.4 years). There were 5 left and 7 right fractures. The fractures were exposed and reduced through the posterolateral elbow approach in 6 patients and through the lateral elbow approach in the other 6 ones. Fixation of all the fractures was conducted with headless double-threaded compression screws plus microplate. At the final follow-up, the elbow function was evaluated by the Mayo elbow performance score and the severity of traumatic arthritis by the Broberg & Morrey imaging criteria. Results All the patients were followed up for 9 to 36 months (average, 23 months). The fracture healing time ranged from 9 to 12 weeks (average, 10.6 weeks). The final follow-ups revealed fine stability of the affected elbow joint in all the patients, and no loss of reduction, loosening or breakage of internal fixators or ischemic necrosis in any case. At the final follow-ups, the elbow inflection angles ranged from 90° to 130° (average, 114.3°), the elbow extension angles from 0° to 20° (average, 12.4°), the forearm pronation angles from 50° to 85° (average, 70.5°) and the forearm supination angles from 45° to 80° (average, 64.3°). The Mayo elbow performance scores at the final follow-up averaged 93.2 points (from 85 to 100 points), yielding 8 excellent and 4 good cases. According to the Broberg & Morrey imaging criteria, 10 patients showed no regressive change and 2 patients change by one grade. Conclusions A proper surgical approach should be chosen according to the preoperative imaging findings. The fracture of articular surface can be firmly fixated by head-less double-threaded compression screws and the integrity of the distal lateral column of the humerus can be restored with a microplate to achieve a strong biomechanical fixation. Fine clinical outcomes can be obtained by early functional exercise. Key words: Elbow joint; Bone fixation, internal; Capitellar fracture; Headless double-threaded screws; Microplate

Comparison of the Pullout Strength of Pedicle Screws According to the Thread Design for Various Degrees of Bone Quality

Although dual-threaded pedicle screws have been developed, the advantages over single-threaded screws remain controversial. We aimed to investigate the biomechanical performance of two types of dual-threaded pedicle screw by comparing their pullout strength with that of a single-threaded screw in relation to bone quality. Four types of pedicle screw with different thread patterns were designed. Type I: single-threaded screw; Type II: double-threaded screw; Type III: dual-threaded screw; Type IV: a newly designed double dual-threaded screw. Five types of polyurethane foams simulating various degrees of bone quality were used. These were: Type A: cancellous bone; Type B: cancellous bone with cortical bone in the upper margin; Type C: osteoporotic cancellous bone; Type D: osteoporotic cancellous bone with cortical bone in the upper margin; and Type E: osteoporotic bone with cortical bone in the upper and lower margins. A comparison of the pullout strength of Type I, II, and III screws in Type A, B, C and D bone specimens was performed. Type C and E bone specimens were used for comparisons among Type I, II, and IV screws. Compared to the single-threaded screw, the dual-threaded pedicle screws exhibited higher pullout strength in normal-quality bone and significantly lower pullout strength in compromised osteoporotic bone. However, the double dual-threaded screw exhibited better pullout biomechanics in osteoporotic bone with bi-cortical bone.

Experimental investigation of cross-laminated timber panels with realistic boundary conditions subjected to simulated blast loads

Recent research efforts have established key dynamic characteristics of cross-laminated timber (CLT) panels and developed parameters that are suitable for analysis and design. Despite such effort, no information is available on the critical role connections play in the behaviour of CLT when subjected to blast loads. The current study investigates a total of thirteen full-scale CLT wall panels with varying connection detailing by simulating the blast loading through a shock tube apparatus. The study found that typical connections with end grain screws into wall elements as well as angled double-threaded screws performed poorly and failed prematurely in tension perpendicular to grain. Reinforcing the connection with screws applied on the panel face did not mitigate the brittle failure. It was found that connection types where the wood is bearing on steel angles or directly on other wood members performed well even when under-designed according to the blast design standard. Whereas thin steel angles provided significant energy dissipation in bending of the angle resulting in reduced panel deflection and damage, thicker steel angles provided the energy dissipation through yielding in the screws as well rotational restraint of the panel ends. Using balloon type assemblies provided significant rotational restraint at the panel ends. The study also found that simplified models developed for idealized simply-supported conditions were not adequate to describe the behaviour of the system.

Factors to improve the efficiency of a vertical screw mixer of bulk materials

The paper shows that it is possible to increase the efficiency of a vertical screw mixer of bulk materials and reduce costs by determining the required size of the feeding hole in the lower part of the casing, as well as by installing a screw flange with a reverse winding in relation to the screw spiral inside the screw casing and by installing a replaceable tip with a variable lead angle at the lower end of the screw. The analysis of the process of screw loading in the hopper allowed us to obtain an analytical dependence to determine the required size of the feeding hole, in which mixed materials freely enter the screw spiral. It is proved that the placement of the screw flange on the inner surface of the casing increases the driving force of material by 1.05 – 1.80 times depending on the screw speed, which significantly reduces specific energy consumption for preparation of mixture of the desired quality. The paper provides the formula for calculating the angle of installation of the flange with respect to the screw spiral, in which the maximum effect of the flange on the mixed materials is obtained. In order to ensure the effective capture of mixed materials in the loading zone of the screw, it is proposed to perform the first spiral turn from the lower end of the screw with a variable lead angle and place it on a replaceable tip. A technical solution to the placement of spirals on the double-threaded screw is also proposed.

A comparative study between double-threaded compression screws and cannulated lag screws for fixation of Garden typeI/IIfemoral neck fractures

Objective To compare the results between double-threaded compression screws and cannulated lag screws for Garden type I/II femoral neck fractures. Methods Data of 56 patients with Garden type I/II femoral neck fractures who were treated with internal fixation from July 2012 to March 2016 were retrospectively analyzed. According to different fixation, the patients were divided into two groups: double-threaded screws group (group A) including 27 cases (7 males and 20 females, with an average age of 55.5±10.0 years, 14 cases Garden type I and 13 cases Garden type II, the proportion of osteoporosis 10/27; And lag screws group (group B) including 29 cases (8 males and 21 females, with an average age of 57.2±9.5 years, 11 cases Garden type I and 18 cases Garden type II, the proportion of osteoporosis 15/29. The 2 groups were compared with respect to bony fusion time, nonunion, avascular necrosis of femoral head, shortening of femoral neck and Harris Hip Score. Results The average follow-up time was 20.3±8.7 m in Group A and 24.5±7.9 m in Group B. The average bony fusion time was 5.3±0.6 m in Group A and 4.1±0.8 m in Group B, and there was significant difference between the groups (t=5.758, P=0.00). 1 avascular necrosis of femoral head was found in both groups. In group A, there were 3 cases of bone nonunion (11.1%, 3/27). There were one bone nonunion (3.4%, 1/29) case in group B, with no statistically significant difference between groups. Shortening of femoral neck occurred in both groups, the average horizontal shortening was 5.8±2.9 mm and vertical shortening 7.0±3.4 mm in Group A, which were lower than group B (8.2±3.1 mm, 9.4±3.6 mm), and the differences showed statistically significant (t=-2.94, P=0.005; t=-2.48, P=0.016) . In group A, the average Harris Hip score was 88.2±8.3, while that in group B was 89.9±7.2. There was no statistically significant difference between two groups. Conclusion It seems to us that in the treatment of Garden type I/II femoral neck fractures, double-threaded compression screws fixation could reduce femoral neck shortening, but there is no difference on functional outcome compared to cannulated lag screws fixation. On the contrary, double-threaded compression screws fixation is not conducive to fracture healing due to lack of sliding compression. Key words: Femoral neck fractures; Fracture fixation, internal; Bone screws

First results with a resorbable MgYREZr compression screw in unstable scaphoid fractures show extensive bone cysts

Osteosynthesis with headless compression screws is an established treatment option for unstable scaphoid fractures. Common implants are made of titanium alloy or steel and usually remain in place. Due to implant density and ferromagnetic properties, artefacts are common in postoperative imaging procedures, e.g. MRI. Now resorbable implants made of magnesium alloy (MgYREZr) have become available. They have biomechanical properties equivalent to human bone and may be used as an alternative to the nonresorbable screw systems.5 patients with acute scaphoid fractures were treated with a double-threaded screw made of MgYREZr. The fractures included three type A2 fractures, one type B2 fracture, and one type B3 fracture. All patients underwent clinical and radiological follow-up postoperatively, 6 weeks, 3 and 6 months and 1 year after surgery. ROM, gross grip strength and pain (VAS) were documented. The Modified Mayo Wrist Score was used. Standard X-rays of the wrist were taken preoperatively and at all follow-up visits. A CT scan was performed at least before and three months after surgery. In all X-rays malunion, resorption of the implant, implant loosening, cysts and bone healing (bridging trabecular structures) were described.All patients had a very good wrist score (95-100 points) after one year. There were no clinical complications. However, the X-rays revealed extensive resorption cysts in 3 out of the 5 patients. It was only after 6 months that the fractures were consolidated enough to allow physical work. Due to this considerable osteolysis, we did not include any further patients. Due to the observed extensive bone cysts and the long time period for bone healing, MgYREZr compression screws are currently not recommended for clinical use in scaphoid fractures. Further fundamental research is necessary.

Development of New Anti-Loosening Bolt Fasteners Based on Coarse-Single Coarse-Multiple Double-Threaded Screw Mechanism

Development of New Anti-Loosening Bolt Fasteners Based on Coarse-Single Coarse-Multiple Double-Threaded Screw Mechanism

Substantiation of design parameters of extruder and determination of extrudate quality

The article reviews the designs of extruders and screws. It describes the main known methods of determination of material quality. As a technical solution improving the design of extruder, a double-threaded screw that should be installed in the material forming zone is proposed.

Experimental Study of Technical Data for Two-Screw Pumps

A brief description is given of a high-efficiency universal industrial two-screw pump, A1 2VV 400/20, with a delivery of 400 m3/h at 20 MPa differential pressure. The results of tests of the pump in oil and water are furnished. Formulas for calculating volumetric and mechanohydraulic efficiency of this pump having double-threaded screws are given. The formulas are derived by processing experimental data in generalized (dimensionless) coordinates and are valid for pumping fluids without free gas. They can be used for rough calculations in the case where gas-liquid mixture is pumped.

Scaphoid nonunions treated with corticocancellous graft and Herbert screw fixation: results at the 10-year follow-up

BackgroundFracture of the scaphoid bone is the most common fracture of the carpus and frequently, diagnosis is delayed as the unique anatomy and blood supply of the scaphoid itself predisposes to delayed union or nonunion. The Herbert screw is a double-threaded screw that provides superior compression compared with other devices used for internal fixation of scaphoid nonunion.ObjectivesThe aim of this study was to evaluate the outcome and presence or progression of degenerative changes in the wrist after corticocancellous bone grafting and Herbert screw fixation.Patients and methodsThis study reviewed 20 patients with scaphoid nonunion who had been operated with a corticocancellous graft and Herbert screw fixation 10 (3.5-11) years previously, all free from arthritic changes preoperatively. The age of the patients at surgery ranged from 17 to 38 years, mean 24.9 years. The interval between trauma and surgery ranged from 8 to 60 months, mean 19.55 months.ResultsThe function of the operated wrist was evaluated according to the scaphoid outcome score (SOS). Only three patients failed to show union. The mean (SOS) was 8.3 (5-10). Flexion was 11.7%, extension was 14.5%, ulnar deviation was 24%, radial deviation was 27.5%, and gripping force was 14.8% to the normal side. Osteoarthritis was present in six patients; this was related to the absence of correction of the preoperatively existing dorsiflexed intercalated segment instability. There was a correlation between the radiological presence of osteoarthritis and the clinical outcome.ConclusionHerbert screw fixation and volar wedge corticocancellous grafting of scaphoid nonunion is a successful operation, with few complications, that produces excellent to good long-term results because of correction of dorsiflexed intercalated segment instability deformity and reduced progression of osteoarthritis in most cases.

Dislozierte Doppelgewindeschrauben nach Densosteosynthese in Knöringer-Technik

A type III fracture of the odontoid process according to Anderson-D'Alonzo in a 92-year-old patient was stabilized anteriorly with two double-threaded screws using the technique of Knöringer. Postoperatively, cranial dislocation of the screws was evident and attempts to correct the screw position failed resulting in screw proximity to the brain stem. In a second revision the screws could be removed by an anterior approach and fusion was achieved by a posterior approach. Type III fractures of the odontoid process are usually stable and should be treated conservatively. In case of instability posterior stabilization techniques should be selected. Anterior osteosynthesis of the odontoid process with double-threaded screws in osteoporotic bone carries the risk of screw dislocation.

Surgical management of a double-layered patella: a case report

The double-layered patella (DLP) is a rare intra-articular disorder that in most cases is associated with multiple epiphyseal dysplasia (MED). The DLP usually consists of an anterior and a posterior layer with a cartilaginous interface between the two parts. In this article, we present a case of bilateral DLP of a 17-year-old female adolescent with MED, suffering clinical symptoms on her left knee. Upon clinical examination, a painful "snapping" of the patella at 30-40 degrees flexion of the left knee was evident and two osseous layers could be identified in standard radiographs. Arthroscopic examination revealed a transient cranial displacement of the posterior osteochondral layer at 30-40 degrees knee flexion that replaced beyond 40 degrees knee flexion with a visible jump. Surgical management in this case of DLP comprised open debridement of the soft tissue interface and fusion of the two osseous layers using double-threaded screws leading to an excellent outcome at 12 months follow-up.